Raw Material of Cosmetics

5 Raw materials of cosmetics

As a result of scientific developments, it is now possible to obtain a diverse range of higher-quality raw materials, including natural compounds, synthetic compounds and biosynthetic materials. Recently, the dominant trends have been disappearance of the dependency on other industries for supply of general raw materials, demand for new functions, and active design of raw materials for cosmetics matching the physiological mechanisms of the skin.

The principal raw materials used to manufacture cosmetics are oily materials such as oils, fats, wax esters, and ester oils, surface active agents used for emulsifiers, solubiliz-ing agents, etc., humectants, thickening agents, film formers, as well as polymers used as powders, ultraviolet absorbents, antioxidants, sequestering agents, coloring agents such as dyes and pigments, along with vitamins, pharmaceutical agents such as plant extracts and perfume.

Cosmetics are generally used only on the skin and hair, consequently the main conditions to be considered when using and selecting the raw materials are: (1) excellent functions matching usage purpose; (2) good safety; (3) excellent oxidation stability; and (4) constant quality such as lack of smell.

The raw materials must be given the above type of consideration but there are also other factors governing the choice of materials such as controls imposed by the laws of various countries (Pharmaceutical Affairs Law). In Japan, new materials that have not received approval for use in cosmetics under the Pharmaceutical Affairs Law cannot be used. To receive approval, the safety of any new materials used in a cosmetic must be confirmed. The majority of approved raw materials for cosmetics are covered by the approximately 2600 entries in the Japanese Standards of Cosmetic Ingredients and Japanese Cosmetic Ingredient Codex. These standards are based on the Cosmetic Quality Standards which govern the quality of cosmetics and establish fixed standards for the raw materials used for the purpose of raising safety; the Japanese Standards of Cosmetic Ingredients describe about 600 raw materials. In America, ingredients that are not prohibited or regulated by law are used at the discretion of the manufacturer.

The following sections explain the principal raw materials used in cosmetics. However, colors and pigments, perfumes, pharmaceutical agents, and preservatives are covered elsewhere in this book and are therefore not explained here.

5.1. Oily materials

Oils have the ability to dissolve fats etc. and are widely used as a component of cosmetics. Oily materials control the evaporation of moisture from the skin and are used mainly to improve the feeling on use.

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122 New cosmetic science

5. LI. Oils and fats

The main components of oils and fats are triglycerides of fatty acids and glycerine which are widespread in the plant and animal kingdoms. Oils are compounds that are liquid at room temperature, while fats are solid^\

Oils and fats used in cosmetics are obtained from nature but they are processed to remove smell and color, etc.; depending on the type, they may be used as hardened oils by partial or complete hydrogenation, or as types with solid fats removed by cooling.

Since oils and fats are obtained either from plants and animals or from living materials, there are many types but a comparatively limited number of them are used as raw materials in cosmetics.

5.1.1.1. Olive oil This oil is pressed from the fruit of the olive tree, Olea europaea Linne. (Oleaceae). The main producing districts are the Mediterranean countries such as Spain and Italy. The constituent fatty acids in the oil are oleic acid (65-85%), as well as palmitic acid (7-16%) and linoleic acid (4-15%).

Olive oil is used to control moisture evaporation from the skin and to enhance the feeling on use.

5.1.1.2. Camellia oil Camellia oil is obtained from the seeds of the camellia bush, Camellia japonica Linne. (Theacea). The constituent fatty acids in the oil are oleic acid (82-88%), as well as saturated fatty acids such as palmitic acid (8-10%) and linoleic acid (1^%).

It is used in cosmetic creams and milky lotions much the same way as olive oil. It has also been long used as hair oil.

5.1.1.3. Macadamia nut oil Macadamia nut oil is pressed from the nuts of the macadamia tree, Macadamia ternifolia in Australia. The constituent fatty acids in the oil are oleic acid (50-65%), as well as palmitoleic acid at unusually high levels (20-27%) for a plant oil. This characteristic improves the feeling on use of cosmetics and macadamia nut oil is widely used in creams, milky lotions and lipsticks ' .

5.1.1.4. Castor oil Castor oil is obtained from the seeds of the castor plant, Ricinus communis Linne. (Euphorbiaceae) and the main producing districts are India and Africa. The constituent fatty acids in the oil are ricinolic acid as the hydroxy acid (85-95%). In comparison to other oils, it is hydrophilic, viscous and soluble in ethanoP^.

These characteristics make it useful in lipsticks and pomades, etc., as well as a dye solvent of tetrabromofluorescein.

5.7.2. Wax esters

In terms of chemical composition, the wax esters are esters of higher fatty acids and higher alcohols; they are obtained from both plants and animals. These plant and animal

Raw materials of cosmetics 123

waxes have many of the same components as esters described previously but they also include free fatty acids, higher alcohols, hydrocarbons, and resins, etc. In addition, the fatty acids and higher alcohols constituting wax esters are different from fats in that they contain relatively more carbon atoms (C20-C30).

Wax esters are used widely in skin care cosmetics and makeup cosmetics, to harden things like lipstick, to give a luster and to improve the feeling on use.

5.7.2.7. Carnauba wax This hard brittle wax is scraped from the leaves and leaf stems of wild or cultivated 10 m high carnauba palms, Copernicia cerifera Mart (Palmae) growing in South America, especially Brazil. It comprises esters of C20-C32 fatty acids, and C28-C34 alcohols; it has large amounts of hydroxy acid esters and has an usually high melting point for a plant waxof80-86°C.

The main uses for carnauba wax are in stick cosmetics such as lipstick to improve the gloss and heat endurance.

5.7.2.2. Candelilla wax This wax is purified from the stems of the candelilla family of Euphorbiaceae plants {Euphorbia cerifera Alcocer, Euphorbia antisyphilitica Zucarrini, and Pedilanthus pa-vonis Boissier) growing in the deserts of northwest Mexico and Texas, etc., which are very dry and experience extreme diurnal variations in temperature. It is composed of approximately 30% C16-C34 fatty-acid esters, and 45% hydrocarbons such as hentriac-ontane (C31H64) with approximately 25% free alcohols such as myricyl alcohol and resins, etc. It is used mainly in stick products such as lipstick to improve gloss and heat endurance.

5.1.2.3. Jojoba oil Jojoba oil is a liquid wax ester extracted from the seeds of the wild jojoba plant, Sim-mondsia chinensis and Simmondsia californica Nuttall (Euphorbiaceae) growing in the high dry deserts of the American south (Arizona, California) and northern Mexico. The main components are esters of unsaturated higher alcohols (11-eicosen-l-ol and 13-dococen-1-ol) as well as unsaturated fatty acids (11-eicosenoic acid and oleic acid)^). In recent years, large amounts have become available from jojoba plantations.

Jojoba oil has excellent stability for autooxidation and superior feeling on use giving it a pleasant touch to the skin so it is used extensively in creams, milky lotions, lipsticks, etc.

5.1.2.4. Beeswax Bees wax is obtained from hives of the Oriental honeybee. Apis indica Radoszkowski (Apidae) and European honeybee, Apis mellifera L.

After the honey is removed from the hive, the wax is put in hot water to separate the bees wax as a yellow or pale yellow solid.

The composition of bees wax from Oriental and European bees is slightly different but the main components are esters of higher fatty acids and higher alcohols with some free fatty acids and hydrocarbons. The main components of bees wax from Oriental honeybees is ceryl 16-hydroxypalmitate (Ci5H3o(OH)COOC26H53) and ceryl palmitate


(C15H31COOC26H53) whereas the main component of bees wax from the European honeybee is miricyl palmitate (Ci5H3iCOOC3iH53)6).

Bees wax is used mainly in creams and stick-type products such as lipstick and hair stick.

5.1.2.5. Lanolin Lanolin is a fatty compound manufactured from the fleece of the domesticated sheep, Ovies aries Linne. (Bovidae). It forms a bright yellow paste.

The main components of lanolin are mixtures of higher fatty acids, sterols and esters of higher alcohols. The constituents of higher fatty acids are a complex mixture of mainly:

Anteiso fatty acids ' ' > CH(CH2)„C00H (w = 4-26)

CH \ ISO fatty acids ' ) CH (CHJ^COOH ( ^ - 6 - 2 4 )

The sterols and higher alcohol components are mainly cholesterol, and isocholesterol but also include C13 to C33 higher alcohols.

Lanolin has an affinity for skin and is quite sticky as well as being physically hygroscopic so it is used in creams and lipsticks.

5.1.3. Hydrocarbons

Hydrocarbons used as raw materials in cosmetics are normally saturated and have carbon chains longer than C15. In the main, they are liquid paraffins, solid paraffins and petrolatum obtained from petrochemical resources, as well as squalane obtained by hydro-genating squalene obtained from both animals and plants.

5.1.3.1. Liquid parajfins Liquid paraffins are manufactured by removing solid paraffins from the petroleum fraction obtained above 300°C.

They are a complex mixture of saturated hydrocarbons with 15-30 carbons and are liquid at room temperature. They are easily manufactured and are colorless, and odorless. They are chemically inactive and form emulsions easily.

They are used in skin care cosmetics such as creams and milky lotions and to control moisture loss from the skin and improve the feeling on use.

5.1.3.2. Paraffin Paraffin is a colorless or white translucent solid (melting point 50-70°C) obtained either by vacuum distillation or solvent extraction of the final fraction remaining in petroleum distillation. It is composed mainly of straight hydrocarbon chains but commonly includes 2-3% branched hydrocarbons. The carbon number ranges from C16-C40 with C20-C30 being most common.


Like liquid paraffins, paraffin is colorless, odorless and chemically inactive and is used widely in creams and lipsticks, etc.

5.1.3.3. Petrolatum The light grease obtained when waxes are removed by solvent extraction from the fraction remaining after vacuum distillation of petroleum is called petrolatum or vaseline. The main component is C24-C34 hydrocarbons in a noncrystalline form. Petrolatum is not a simple mixture of liquid paraffins and paraffin; it is believed to be a colloid composed of external phase solid paraffin and internal phase liquid paraffins.

Like liquid paraffin, petrolatum is odorless, chemically inactive and has high adhesive power so it is used widely in creams and lipsticks, etc.

5.1.3.4. Ceresin Ceresin is refined ozocerite and it is mainly composed of C29-C35 straight hydrocarbons although it sometimes includes isoparaffin. The molecular weight is higher than that of paraffin and the specific gravity, hardness and melting point (61-95°C), etc., are high.

It is used as a hardening agent in lipsticks, hair sticks, etc.

5.7.5.5. Microcrystalline wax Microcrystalline wax ^ is a solid obtained by extracting the oil from petrolatum. It is a complex mixture composed mainly of C31-C70 isoparaffins.

It has a microcrystalline structure, high adhesive power, good extensibility, is not susceptible to low temperatures, and a high melting point (60-85°C). When mixed with other waxes, it suppresses crystal formation making it useful in lipsticks and creams.

5.1.3.6. Squalane Squalene occurs in large amounts in various species of deep sea sharks and it is also found in olive oil, etc. Squalane (2,6,10,15,19,23-hexamethyltetracosan, C30H62) is obtained by hydrogenating squalene; it is liquid at room temperature.

Squalane is a very safe, chemically inactive oil used widely in skin care cosmetics such as creams and milky lotions, etc.

5.1.4. Higher fatty acids

Fatty acids are compounds with the general chemical formula RCOOH where R is either a saturated alkyl group or an unsaturated alkenyl group. They include various esters in natural fats and oils. Fatty acids in various plant and animal fats have many straight chain carbon molecules and are almost all even numbered. However, progress in petrochemical synthesis has led to the development of side chain and odd number fatty ac-ids8).

Fatty acids are mixed with fats and oils, waxes and hydrocarbon compounds for use as raw materials of cosmetics. They are also used with caustic potash and triethanola-mines, etc., as emulsifiers for the production of soaps.

5.1.4.1. Laurie acid: CHs(CH2)ioCOOH Laurie acid is obtained by distillation of the fatty acid mixture obtained by saponifica-


tion of coconut and palm nut oils. Soap obtained by mixing lauric acid with sodium hydroxide and triethanolamine has high solubility in water and lathering qualities making it useful for cosmetic soaps and cleansing preparations.

5.1.4.2. Myristicacid: CHs(CH2)i2COOH Myristic acid is obtained by distillation of the fatty acid mixture obtained by saponification of palm nut oil. It is not used directly to any great extent in cosmetics but myristic acid soap has excellent lathering qualities and cleansing power so it is used in cleansing preparations.

5.1.4.3. Palmitic acid: CHi(CH2)i4COOH Palmitic acid is obtained by saponification of palm oil, etc. It is used as a oily base in creams and milky lotions, etc.

5.1.4.4. Stearic acid: CH3(CH2)i6COOH There are two manufacturing processes for stearic acid: (1) production by removing liquid acids (mainly oleic acid) from the fatty acids obtained by saponification of fat from beef tallow, and (2) production by distillation of fatty acids obtained by saponification of hydrogenated soy bean or cotton seed oil. Stearic acid obtained by the former method contains quite a lot of palmitic acid, whereas the latter method produces stearic acid of high purity and high melting point .

Stearic acid is used in creams to modify the cream consistency and hardness; it is common in creams, lotions and lipsticks, etc.

5.1.4.5. Isostearic acid The Cig saturated fatty acid with a branched structure is called isostearic acid. Isostearic acid is formed by hydrogenation of the unsaturated fatty acid byproduct when synthesizing dimer acid from oleic acid^\ It can also be produced by the Guerbet method and by hydrogenating and oxidizing the aldol condensate of nonyl aldehyde.

Isostearic acid is a liquid ingredient with a lower melting point than saturated fatty acids like stearic acid and palmitic acid and it is less easily oxidized than unsaturated fatty acids such as oleic acid. It is used as an oily raw material and the salts such as triethanolamine are used as emulsifiers.

5.7.5. Higher alcohols

Higher alcohol is the name given to monovalent alcohols with six or more carbon atoms. They are broadly grouped into alcohols produced from natural oils and fats and alcohols produced from petrochemicals^^^

The higher alcohols are used both as oily raw materials and as emulsion stabilizers in emulsified products.

5.7.5.7. Cetyl alcohol^^\' CHs(CH2)i50H Cetyl alcohol is also called cetanol and it is produced by fractional distillation of the alcohols obtained by saponification of whale oil. It can also be produced by fractional distillation after reduction of fat from beef tallow, as well as by the Ziegler reaction.


Cetyl alcohol is a white waxy solid with a hydroxyl group so it does not have emulsifying properties itself but is used as an emulsion stabilizer in emulsified products such as creams and milky lotions.

5.7.5.2. Stearyl alcohol: CH3(CH2)i70H Stearyl alcohol is manufactured by the same method as cetyl alcohol. It is a white waxy solid. It is used both as an emulsion stabilizer in emulsified products such as creams and milky lotions, and in stick products such as lipsticks.

5.1.5.3. Isostearyl alcohol Isostearyl alcohol is the name given to the Cig saturated alcohol with a branched structure. It is obtained by chemical synthesis using the Guerbet reaction, the oxo reaction and by aldol condensation, etc. In recent years, isostearyl alcohol produced by reduction of isostearic acid formed by hydrogenation of unsaturated fatty acid byproducts of dimer acid production has appeared on the market.

Isostearyl alcohol is a liquid ingredient with excellent heat and oxidation stability; it is used as an oily raw material.

5.1.5.4. 2-Octyl dodecanol 2-Octyl dodecanol is synthesized by the Guerbet reaction and by aldol condensation.

It is a colorless transparent liquid with almost no smell and a low freezing point due to its branched structure which is unusual in higher alcohols. It has good feeling on use so it is used as an oily raw material.

5.1,6. Esters

Esters are obtained by dehydration of acids and alcohols. Typical acids are fatty acids, polybasic acids, and hydroxy acids; typical alcohols are lower and higher alcohols, and polyhydric alcohols. Various esters are produced from different combinations of acids and alcohols but relatively few are used in cosmetics.

Esters have different properties depending on the structure, molecular weight, etc., and they are used as emollients, dye solvents and clouding agents, etc.

5.1.6.1. Isopropyl myristate Isopropyl myristate is a colorless transparent liquid produced by esterification of myris-tic acid and isopropanol under sulfuric acids followed by distillation and deodorization.

It is used as a miscible agent for oil and water mixtures, as a solvent for dyes, etc., and in milky lotions, makeup products and hair cosmetics.

5.1.6.2. 2-Octyldodecyl myristate 2-Octyldodecyl myristate is an ester of myristic acid and 2-octyldodecanol obtained by the Guerbet reaction.

It has a low melting point and is very resistant to hydrolysis. It is used to control moisture loss from the skin as well as to improve the feeling on use.


5.1.6.3. Cetyl 2-ethyl hexanoate Cetyl 2-ethyl hexanoate is an ester of cetanol and 2-ethylhexanoic acid. It has a low viscosity and high resistance to hydrolysis and oxidation, as well as a good feeling on use so, it is used widely in creams, milky lotions, etc.

5.1.6.4. Di-isostearyl malate Di-isostearyl malate is an ester of isostearyl alcohol and malic acid. It is a thick transparent liquid in spite of its high molecular weight. The isostearyl alcohol used in this production is composed mainly of 5,7,7-trimethyl-2-(l,3,3-trimethylbutyl) octyl alcohol.

Di-isostearyl malate is very resistant to hydrolysis and oxidation. It has a relatively low stickiness in spite of its high viscosity. It is excellent as a dispersant and miscible agent for pigments, and also as a miscibilizer for polarized-nonpolarized oily mixtures such as castor oil and liquid paraffin. As a result of these characteristics it is used in stick products such as lipstick, as well as in foundations and creams.

5.7.7. Silicones

Silicones is the name given to organic silicon compounds containing the siloxane chain (-Si-O-Si-). A typical example is methylpolysiloxane in which all the organic groups are methyl groups. The silicones are available in a wide range of viscosities. Silicones are highly hygroscopic and they have none of the sticky feeling found in hydrocarbons so they have good feeling on use making them suitable for a wide range of applications on skin and hair. Two typical silicones are described below. - ^

5.1.7.1. Dimethylpolysiloxane

CH3 I -

CHa-Si -O I

CH3

CH3 I

-Si-0 I

CHa

CH3

I -Si-CHa

I CH3

Dimethylpolysiloxane is a colorless transparent oil. There are low-viscosity oils and pastes depending on molecular weight. Since the solubility of other materials worsens with increasing molecular weight, such low-viscosity materials have many applications. The high hygroscopy makes dimethylpolysiloxane useful in skin cosmetics for resisting fade of make up caused by water and perspiration. Dimethylpolysiloxane reduces the stickiness of oils giving a light feeling on use; it is also employed in a wide range of skin and hair products due to its spreadability.

5.1.7.2. Methylphenylpolysiloxane Methylphenylpolysiloxane has a structure in which some of the methyl groups of dimethylpolysiloxane are replaced by phenyl groups. It is characterized by complete insolubility in ethanol. However, it has good compatibility in other oils and is used in a wide range of products.


5.7.8. Others

Polyoxypropylene adducts of the lower alcohols like butanol are used in liquid hair dressings.

The adducts are obtained by addition of propylene oxide to lower alcohols with an alkaline catalyst such as sodium hydroxide.

Comparatively low molecular weight adducts are soluble in ethanol and liquid at room temperature. They are used in liquid hair dressings due to their ability to keep hair neat and tidy.

5.2. Surface active agents

The solute in a solution can be adsorped to a gas-liquid, liquid-liquid, or liquid-solid surface; these remarkable changes in the properties of surfaces are called surface activity and so-called surface active agents are materials demonstrating unusual surface activity.

This surface activity is exploited in emulsification, solubilization, permeation, wetting, dispersion, cleansing, as well as in moisturizing, sterilization, lubrication, electrostatic prevention, softening, antifoaming, etc.

There are a very large number of surface active agents but they share a similar molecular structure; the molecule has a part with an affinity for oils (lipophilic or hydrophobic) and a part that has an affinity for water (hydrophilic). The combination and balance of these causes various changes in the properties of the interface or surface. Surface active agents (surfactants) are classified in various ways according to chemical structure, synthesis method, properties and uses, etc. However, generally the major classification is based on the ionic dissociation when dissolved in water. Dissociating types are classified as anionic, cationic and amphoteric types, whereas non-dissociating types are classified as non-ionic. The following section describes some typical surfactants based on this classification as well as some polymeric and natural surfactants.

5.2.1. Anionic surfactants

When anionic surfactants are dissolved in the water, the hydrophilic base dissociates into anions; anionic surfactants are classified broadly into carbonate, sulfate ester, sulfonate and phosphate ester types. Generally, a soluble salt such as sodium, potassium, or triethanolamine is used as the hydrophilic part. A great many compounds can be used as the lipophilic part but generally alkyl or branched alkyl groups are used. Consequently, the molecular structure incorporates acid-amide bonds, ester bonds and ether bonds, etc.

Typical anionic surfactants are described below.

5.2.7.7. Soap: RCOOM [R: Cy_2i> M: Na, K, N(CH2CH20H)s] Soaps are obtained by hot saponification of an alkaline aqueous solution of fats such as tallow fats, coconut oil and palm nut oil; the reaction between higher fatty acids and alkali creates a so-called neutral soap. Soaps are widely used in cosmetics as cleansing creams and shaving creams due to their excellent cleansing and lathering properties.


5.2.1.2. Alkyl sulfate: ROSOjM Alkyl sulfates are obtained by reacting fatty alcohols with chlorosulfonic acid, sulfuric anhydride, or fuming sulfuric acid, etc. and then neutralizing.

They are used in such cosmetic products as shampoos and dentifrices due to their excellent cleansing and lathering properties.

5.2.1.3. Polyoxyethylene alkyl ether sulfate: RO(CH2CH20)^SOsM Polyoxyethylene alkyl ether sulfate is obtained by polymerizing oxyethylene and a fatty-acid alcohol by addition polymerization followed by sulfonation and neutralizing with an alkali. The solubility is good and it is used widely in shampoos, etc., due to its excellent cleansing and lathering properties. The alkyl group is C12-C14 and two or three moles of oxyethylene give improved lathering and cleansing.

5.2.1.4. Acyl N-methyl taurate

R • CONCH2CH2SO3M I

CH3

Acyl A -methyl taurate is obtained by a dehydrochloric acid reaction under alkaline conditions of an acyl chloride and methyl tauric acid, or by a dehydration reaction between a fatty acid and methyl tauric acid. It is very safe and usable in wide pH range and in hard water as well as good lathering properties so it is widely used in cosmetic cleansing creams, shampoos, etc.

5.2.1.5. Alkylether phosphate

KOxpÔ R O ^ ^ ^ O RO^^Ô

MO"" ÔM RO"" ÔM RO^ ^ OR

Monoalkyl ether phosphate Dialkyl ether phosphate Trialkyl ether phosphate

Alkylether phosphate is obtained by phosphoric esterification of a fatty alcohol or the terminal group of the polyoxyethylene derivative and then subsequent neutralization. The product on the market is actually a mixture of the mono-, di- and trialkyl ether phosphate. The monoalkyl ether phosphate is soluble in water but the trialkyl ether phosphate is only slightly soluble so this surfactant must be selected according to product usage. Alkylether phosphate is used in cosmetic cleansing creams and shampoos.

5.2.1.6. N-Acylamino acid salts Since amino acids have both amino and carboxyl groups in the molecule, it is possible to obtain surface activity by introducing a lipophilic material. A typical substance is A''-acylamino acid salt which is obtained from a reaction with a fatty acid. Examples are N-Acylsarcosinate RCON(CH3)CH2COOM, A^-acyl-A^-methyl-/?-alaninate RCONCCHg)-CH2CH2COOM, and A^-Acylglutamate RCONHCH(COOM)CH2CH2COOM.


Since A^-acylglutamate has two carboxyl groups in the molecule, it is possible to obtain surfactants containing mono- or di- salt with any ratio. This A^-acylglutamate is used in shampoos, cleansing creams and dentifrices.

5.2.2. Cationic surfactants

When a cationic surfactant is dissolved in water, the hydrophilic part dissociates as cations. Since this is the reverse of anionic surfactants, these materials are called invert soaps. Cationic surfactants have normal surface activities such as cleansing, emulsifica-tion and solubilizing, but they are especially well adsorbed onto smooth hair and also have anti-static properties, so they are used in hair treatments.

Cationic surfactants are classified from their structure into quaternary ammonium salts and amine derivatives but the amine derivatives are hardly used in cosmetics and are omitted from this discussion.

5.2.2.7. Alkyltrimethyl ammonium chloride: (RN-^(CHj)j)Cl~ R: Cj^C22 Alkyltrimethyl ammonium chloride is obtained as the quaternary ammonium salt via the alkyldimethyl amine produced by reacting an alkyl amine with methyl chloride in an alkaline medium under pressure.

5.2.2.2. Dialkyl dimethyl ammonium chloride: (R'R'N^(CHj)2)Cl~ R: Ci^C22 This compound is known to have smoothing properties on tangled hair and also has antistatic properties, so it is used in hair rinses. It has poor bactericidal activities but low toxicity and skin irritability.

5.2.2.3. Benzalkonium chloride

CH3

^ ^ C H - N ^ - R

CH3

c i - C R : C . 3 ~ M ]

This compound is well known as an invert soap and it is generally used as a bactericide particularly in shampoos, hair tonics and hair rinses.

5.2.3. Amphoteric surfactants

Amphoteric surfactants have both cationic and anionic functional groups coexisting in the molecule. Generally, under alkaline conditions, they dissociate into anions, and under acid conditions, into cations.

For this reason, they can be used to make up for the deficiencies of ionic surfactants. In comparison to ionic surfactants, they have very low skin irritability and toxicity and many amphoteric surfactants have good cleansing, bactericidal, bacteriostatic, lathering, and softening properties. These properties are used to advantage in shampoos and baby products; in addition, they are used in aerosols due to their ability to stabilize the lather and promote its formation.


5.2.3J. Alkyl dimethylaminoacetic acid betaine: RN^(CHj)2CH2COO- R: Cj2-C]8 As shown by the above structure, the surface activity of this compound is due to the combination of a cationic quaternary ammonium salt and an anionic carboxyl group. A characteristic feature of alkyl dimethylaminoacetic acid betaine is its good solubilization ability and stability across a wide pH range. In cosmetics, it is used in shampoos and hair rinses due to its softening, anti-static and wetting properties.

5.2.3.2. Alkyl amidopropyl dimethylaminoacetic acid betaine: RCOONH(CH2)3N^. (CHs)2CH2COO-This compound is also used in shampoos, etc., due to its softening, anti-static and wetting properties.

5.2.3.3. 2-Alkyl-N-carboxymethyl'N-hydroxyethylimidazolinium betaine

R-cr^ I ^N^-CH2

/ \ -OCOCH2 CH2CH2OH

The above structural diagram shows that this compound has an imidazolin ring and it has recently been elucidated that the ring is open rather than closed^^^ Like other amphoteric surfactants, this compound has very low toxicity, skin irritability and mucous-membrane irritability and also makes the hair softer and more glossy. In addition, it is able to tolerate hard water, making it ideal for use in hair cosmetics, creams and emulsions, etc.

5.2.4. Non-ionic surfactants

Non-ionic surfactants are unlike ionic and amphoteric surfactants because they do not dissociate into ions.

Their surface activity is due to the presence of -OH, - 0 - , -CONH-, and -COOR groups in the molecule. Owing to this structure, they are generally classified into polyoxyethylene chains having hydrophilic groups, and compounds with hydroxyl groups. In other words, the lipophilic groups are broadly the same as the ionic surfactants, but there are many possible combinations of types ranging from those with low water solubility, due to the length of the polyoxyethylene chain containing the hydrophilic groups, to those with good water solubility due to the number of hydroxyl groups. These combinations cause large differences in properties such as degree of solubility, wetting, penetration power, emulsification and solubilization, etc., of non-ionic surfactants due to the different balances (HLB) of lipophilic and hydrophilic groups.

5.2.4.1. Polyoxyethylene type non-ionic surfactants

RO(CH2CH20)„H R: C12-C24 RCOO(CH2CH20)„H R: C12-C18 RC6H60(CH2CH20)„H R: C8-C9


As the formulae show, these compounds are obtained by addition polymerization of ethylene oxide at normal or elevated pressures in an alkaline medium. The lipophilic groups are typically a higher fatty alcohol, a higher fatty acid, an alkyl phenyl, an alkylolamide or a sorbitan higher fatty-acid ester, etc. Since they are obtained by addition polymerization of ethylene oxide, normally, various types with a degree of polymerization are obtained rather than simple compositions. The solubilization of these surfactants in water can be evaluated by measuring the clouding point. If the lipophilic group is the same, the clouding point becomes higher as the length of the polyoxyethylene chain increases and they become more hydrophilic. Since these types of surfactants have excellent emulsifying and solubilizing abilities, these are used as emulsifiers in creams and milky lotions, and as solubilizers for perfumes and pharmaceutical agents, etc., in lotion.

5.2.4.2. Polyhydric alcohol ester type non-ionic surfactants These surfactants are produced by converting fatty acid esters of some of the hydroxyl groups of polyhydric alcohols, starting from glycerin, to fatty-acid esters and leaving the residual hydroxyl groups as hydrophilic groups. For example, monoglycerides are produced by esterification; they can also be produced by ester conversion from fats and glycerin. The best polyhydric alcohols to use are glycerin and trimethylol propane with three hydroxyl groups, pentaerythritol and sorbitan with four hydroxyl groups, sorbitol with six hydroxyl groups, and sucrose with eight hydroxyl groups. They can also be synthesized to compounds with several ester bonds from monoesters using the above-described reaction from polyglycerin and raffinose, etc., with even more hydroxyl groups. Typical examples in this group are mono or diglycerides, sorbitan higher fatty-acid esters, and sucrose higher fatty-acid esters, etc. Most of these types are hydrophilic to some extent and form emulsions in water; monoglycerides are combined with hydrophilic surfactants and used in cosmetics. Moreover, several HLB type non-ionic surfactants can be produced by addition polymerization of appropriate ethylene oxide to the residual hydroxyl groups. For example, such surfactants can be produced by addition polymerization of appropriate ethylene oxide to the residual hydroxyl groups of the sorbitan higher fatty-acid monoester and hardening with natural castor oil as well as by ethylene oxide addition. These surfactants show good emulsifying and solubilizing ability so they are widely used in skin care cosmetics.

5.2.4.3. Ethyleneoxide-propyleneoxide block polymers

CH3

HO (CH2 CH2O). (CH CH^On (CH2 CH2O), H

(m + n + m = 20—80, n = 15—50)

Ethyleneoxide-propyleneoxide block polymers contain both lipophilic groups glycol and hydrophilic groups from polyethylene glycol, so various surfactants having different HLBs can be obtained by freely changing m and n in the above chemical formula. These compounds have a comparatively larger molecule than other surfactants and are characterized by low skin irritation. They are marketed under the brand name Pluronic and are used widely.


5.2,5. Other surfactants

5.2.5.1. Polymeric surfactants Many early surfactants contained about 10-18 carbon atoms as the lipophilic group and had a molecular weight of about 300. If ethylene oxide propyleneoxide block polymers are combined with many polyoxyethylene, it is possible to obtain a molecule with a weight of 1000-2000 but normally the molecular weight is less than 1000.

Based on this, polymeric surfactants could be described as surfactants with a high molecular weight. For example, polyvinyl alcohol can be made into fiber and film but when it is used for the action of emulsification or coagulation, it could easily be described as a polymeric surfactant. Based on this concept, sodium alginate, starch derivatives, and tragacanth gum, etc., can be used as emulsifiers, flocculants and dispersants.

5.2.5.2. Natural surfactants Lecithin is a well-known natural surfactant combining the anionic groups of phosphate esters with the cationic groups of quaternary ammonium salts. Lecithin is obtained from soy beans and egg yolks and the main components are phosphatidyl serine, phosphatidyl ethanolamine, phosphatidyl choline. In cosmetic applications, lecithin is used in milky lotions and creams because it has a refreshing feeling on use and softening properties. Recently, lecithin has been used to form liposomes which have a bilayer membrane.

Many other natural surfactants have long been known and used including lanolin, cholesterol and saponin.

5.3. Humectants

Maintaining a young-looking skin is closely connected with moisture content ' ^^ One of the most important functions of cosmetics is maintaining skin moisture^^ .

The keratin layer of the skin contains natural moisturizing factors - ^^ (NMF) with hydrophilic moisture absorbing compounds; NMFs are known to play an important role in skin moisturizing (Table 5.1). It is believed that the sodium salt of sodium pyrrolido-necarboxylate is the most important factor in NMF^ ' ^^

NMF is not the only important factor in considering skin moisture; it is also important to consider preventing loss by bonding or surrounding, the presence of oils such as intercellular lipids and sebum controlling moisture evaporation, and holding water, the presence of mucopolysaccharides in the dermis. Cosmetics should be able to mimic this natural moisture retention mechanism. Humectants are water soluble materials with a high water absorption and they are a very important component in the aqueous phase of cosmetics.

A wide variety of humectants are used in cosmetics including polyhydric alcohols like glycerin, propylene glycol, sorbitol, and including the main component of NMF, pyr-rolidonecarbonate and lactates. Recent advances in biosynthesis technology has also permitted production and use of large amounts of sodium hyaluronate. As described previously, humectants play an important role in cosmetics but at the same time they also work to maintain the moisture content and stabilize the cosmetic itself. In addition, they also have bacteriostatic and fixative activities.


Table 5.1. Composition of NMFi , )

Amino acids

PCA(pyrrolidone carboxylic acid)

Lactates

Urea

NH3, uric acid, glucosamine, creatinine

Citrates

Na 5%, K 4%, Ca 1.5%, Mg 1.5%, PO4 0.5%, CI 6%

Sucrose, organic acids, peptides, other materials

40%

12%

12%

7%

1.5% 0.5%

18.5%

8.5%

(O.K. Jacobi : Proc. Sci. Sec. of Toilet Goods Assoc, 31, 22, 1959.) (H.W. Spiet, G. Pascher : Hautarzt, 7, 2, 1956.)

The main requirements of a humectant are listed below: (1) must have appropriate water absorption ability (2) must maintain water absorption ability (3) water absorption must not be influenced by changing environmental conditions

(temperature, humidity, etc.) (4) water absorption ability must maintain moisture in skin (5) must have lowest possible volatility (6) must have good miscibility with other constituents (7) must have lowest possible freezing point (8) viscosity must match usage and feel good on skin (9) must be safe (10) must be as colorless, odorless and tasteless as possible

In addition to having water absorption and moisturizing properties over a wide range of humidities, humectants must have densities matching the system they are used in. Even when the humectant is used incorrectly, the correct functions must still be maintained and reverse effects should not be possible.

5.3.1. Glycerin

CH2OH

CHOH I

CH2OH

Glycerin has long been used as a humectant and it is still widely used even today. It is obtained as a byproduct in manufacturing soap or fatty acids from plant and animal fats and oils. When dehydrated and deodorized, it is a colorless, odorless liquid.

5.3.2. Propylene glycol

CH3 I

CHOH I

CH2OH


The common form is 1,2-propylene glycol. Although it looks and feels much like glycerin and is colorless and odorless, it has a better feeling on use due to its lower viscosity than glycerin.

5.3.3. 13-Butylene glycol: CHsCH(OH)CH2CH20H

1,3-Butylene glycol is obtained by hydrogenation of the aldol condensate of acetoalde-hyde as a colorless, odorless liquid. It is very safe and is used in creams and milky lotions, etc.

5.3.4. Polyethylene glycol: HO(CH2CH20),H

Polyethylene glycol is obtained by adding ethylene oxide to water or ethylene glycol under alkaline conditions. It is not a uniformly simple compound but is a mixture polymer with various degrees of polymerization.

It is a liquid at normal temperatures with an average molecular weight ranging from 200 to 600; semi-solid forms have increasing molecular weights ranging from 1000, 1500, 4000 to 6000.

Generally, polyethylene glycol is colorless and odorless and its water absorption ability decreases with increasing molecular weight. It is used in creams, milky lotions, etc.

5.3.5. Sorbitol

CH2OH I

(CH0H)4 I

CH2OH

This sugar alcohoP^^ is contained in the juice of apples and peaches, and is a white odorless solid. It is obtained by reduction of glucose.

In comparison to the previously described humectants, it has lower hygroscopic property and it has a humectant effect at low humidity. It is used in creams, milky lotions, toothpastes, etc.

5.3.6. Sodium lactate: CH^CHiOHjCOONa

Lactates are an important group of natural humectants occurring in NMF along with PC A (pyrrolidonecarboxylate). They have a higher water absorption ability than the lower-alcohol types.

5.3.7. Sodium 2-pyrrolidone-5-carboxylate

CH2~CH2

0 ^ ^ \ N^ ^COONa H


Table 5.2. Water absorption ability of sodium 2-pyrrolidone-5-carboxylate ^^

Compound

Pyrrolidone carboxylic acid

Sodium pyrrolidone carboxylate

Gylcerol (comparison)

31% RH

< 1

20

13

58% RH

< 1

61

35

(K. Ladem, R. Spitzer : J. Soc Cosmet. Chem., 18, 351, 1967.)

Sodium 2-pyrrolidone-5-carboxylate is an important humectant component of NMF. It is the sodium salt of 2-pyrrolidine-5-carboxylate manufactured by dehydration of glutamic acid and forms an odorless solid.

It demonstrates excellent hygroscopic and humectant effects and these properties have been achieved with a salt form (Table 5.2).

5,3.8. Sodium hyaluronate

Hyaluronic acid is a type of mucopolysaccharide formed by cross-bonding between A -acetylglucosamine and gluconic acid. It is widely found in connective tissues of mammals as chondroitin sulfate, etc. In connective tissues, its function is to maintain water in the intercellular spaces and also to maintain the cells in a jelly matrix. In skin, it is believed to maintain smoothness and flexibility and to prevent external mechanical injury and bacterial infection. When examining the distribution of acidic mucopolysaccahrides in the different parts of the skin, more hyaluronic acid exists than chondroitin sulfate and heparin in the epidermis and dermis. Having moisturizing properties, hyaluronic acid makes the skin feel nice and moist; it is said that skin lacking moisture develops wrinkles due to the shortage of moisturizing hyalouronic acid in the subdermal connective tissues.

Hyaluronic acid was extracted from the cockscomb of domestic fowls, but its extremely high price greatly limited use until recent development of production by microbiological techniques provided a relatively low-cost source ' ^ .

Generally, hyaluronic acid is marketed as sodium hyaluronate, a white water-soluble powder. Properties like viscosity and humectance vary with the molecular weight. The water evaporation constant of a 0.1% aqueous solution of sodium hyaluronate at 25°C and 50% relative humidity falls with increasing molecular weight but stabilizes at molecular weights above about 800,000^^).

In addition, unlike other humectants, sodium hyaluranate is almost unaffected by environmental humidity (Fig. 5.1).


100

03

B

•5 q U)

50

J Iff / f c t t H M 1 I I I I I

Moisture absorbance/^ Relative humidity Temperature 33%

Fig. 5-1. Comparison of Moisture Absorbance of Humectants

1^^^ Sodium pyrrolidone carboxylate f:-:':':'| Glycerine I I Sorbitol \IW\W\ Sodium hyaluronate

Fig. 5.1. Comparison of moisture absorbance of humectants.

5.4. Polymers

Polymers ' ^^) used as cosmetic raw materials are basically classified according to usage. They are mainly used as thickening agents, film formers and resinous powders. In addition, some polymers are used as humectants and surfactants. This section describes only thickening agents and film formers; the humectants, surfactants and resinous powders are described in their respective sections.

5.4.L Thickening agents

Thickening agents are used to adjust the viscosity of products to make them easy-to-use as well as to maintain the product stability.

For example, they are used to ensure the stability of milky lotions and liquid foundations by preventing the separation of emulsified particles and powders. Usually, water-soluble polymers are used as thickening agents. Table 5.3 shows the major classification based on their origin. They are classified into natural polymers, semi-synthetic polymers (natural polymers modified by reaction) and synthetic polymers. However, in the past, natural polymers formed the mainstream led by natural gums. Problems with securing stable supplies coupled with problems such as variations in viscosity and microbial contamination led to a change to synthetic and semi-synthetic substitutes. Currently, synthetic thickening agents are in the majority. Thickening agents have a great effect on the feeling on use


Table 5.3. Classification of water-soluble polymers

I—Vegetable

(mucopolysaccharides)

Water-

soluble -

polymer

-Organic —

-Natural polymer-

-Microbial-

(mucopolysaccharides)

-Animal

(proteins)

I—Celluloses

-Guar gum, Locast bean gum,

Quince seed gum, Carrageenan,

G a l a c t a n , Gum A r a b i c ,

Tragacanth gum. Pectin, Man-

nan, Starch

-Xanthan gum, Dextran, Suc-

cinoglucan, Hyaluronic acid

-Gelatin, Casein, Albumin, Col

lagen

-Semi-synthetic-polymer

-Synthetic polymer-

Methyl cellulose, Ethyl cellu

lose, Hydroxyethyl cellulose,

Hydroxypropyl cellulose, Car-

boxymethyl cellulose, Methyl-

hydroxypropyl cellulose

-Starches Soluble starches, Carboxymeth-

yl starch. Methyl starch

I—Alginates Propyleneglycol ester alginate.

Alginates

'—Other mucopolysaccharide derivatives

Vinyls Polyvinyl alcohol. Polyvinyl

pyrrolidone, Polyvinylmethyl

ether, Carboxyvinyl polymer.

Sodium polyacrylate

L-Other-

-Inorganic-

-Polyethylene oxide. Ethylene

oxide-propylene oxide copoly

mers

-Bentonite, Laponite, Silicate

powders. Colloidal alumina

of cosmetics, and various water-soluble polymers are in widespread use according to purpose.

5.4.1.1. Quince seed gum Quince seed gum is a natural gum obtained from the seeds of the quince tree growing in Europe and S. Asia. It is an acidic polysaccharide composed of L-arabinose, D-xylose, glucose, galactose, and uronic acid. To extract it, quince seeds are soaked in 20 times their weight of water (approx. 60°C) and left to soak overnight, stirring occasionally, and then filtered. The seeds are then put into a tank and the procedure is repeated. A liquid of the right viscosity is produced by mixing these liquids. This viscous liquid has a characteristic non-sticky smooth feeling. It is easily contaminated by microbes so it must either be sterilized or a preservative must be used.

5.4.1.2. Xanthan gum Xanthan gum is a natural gum obtained by fermentation of glucose with Xanthomonas campestris. It is an acidic polysaccharide composed of D-glucose, D-mannose, and D-


glucronic acid. It has excellent usage characteristics due to low temperature dependence and stability over a wide pH range.

5.4.1.3. Sodium carboxymethyl cellulose Sodium carboxymethyl cellulose is a semi-synthetic polymer obtained by partial substitution of the hydroxyl groups in cellulose with -0CH2C00Na groups and dissolution in water. It is a transparent viscous liquid with protective colloidal and emulsification stability making it useful in creams, milky lotion and shampoos, etc.

5.4.1.4. Carboxyvinyl polymer Carboxy vinyl polymer is synthetic aery late polymer with carboxy 1 groups. It is an aqueous liquid with remarkable viscosity at neutral pH (by NaOH, KOH, triethanol amine). The quality is very stable and there is almost no change in viscosity over time or with temperature; it is much less easily contaminated by bacteria, etc., than natural gums, so it is widely used as a thickening agent.

5.4.2. Film formers

As shown in Table 5.4, film formers are found in a wide range of products. Film formers are classified into water-and alcohol-soluble types according to solubility, as well as into aqueous-emulsion and non-aqueous soluble types. Packs are made by usage of film forming ability after vaporizing the water from an aqueous solution of polyvinyl alcohol. Hair sprays and hair setting lotion use polymers dissolved in water or alcohol to form a film which sets the hair. Although the polymers in shampoos and rinses do not really have a film forming function, cationic polymers are used to improve the feeling on use. Eye liners and mascara contain an aqueous polymer emulsion which uses the formed water-proof film to resist fade of makeup caused by tears and perspiration. Typical film formers are not soluble in water. In nail enamels nitrocellulose is dissolved in butyl or ethyl acetate and in split hair coatings, a silicone polymer is dissolved in a volatile oil to give a protective coating to the hair. In addition, silicone resin is also used for its film forming properties in long lasting cosmetics such as sun oils and liquid foundations.

5.4.2.1. Polyvinyl alcohol (PVA)

-CH2-CH-f-I OH n

Completely saponifide

CH2-CH-I OH

-CH2-CH— I 0

I c=o

I CH3

Partially saponifide

PVA is manufactured by saponification of polyvinyl acetate; the viscosity and film strength vary with the degree of saponification and polymerization.


Table 5.4. Film forming products and typical raw materials

Solubility of Film Formers

Water

(alcohol)

Aqueous emul

sion

Non-aqueous

Product type

Packs

Hair spray, Hair setting

preparations

Shampoo, Rinse

Eye liner, Mascara

Nail enamel

Split hair coatings

Sun oil, Liquid founda

tion

Typical raw material

Polyvinyl alcohol

Polyvinyl pyrrolidone, methoxyethylene anhydrous malate

copolymer. Amphoteric methacrylate ester copolymer

Cationic cellulose, Polychlorinated dimethylmethylene

piperidinium

polyacrylate ester copolymer

Nitrocellulose

Silicone gum

Silicone resin

The most commonly-used form is about 90% saponified material due to its good solubility and solution stability. In addition to being used to form films in packs, its colloid maintaining properties are also used to stabilize emulsions.

5.4.2.2. Polyvinyl pyrrolidone

/

I -CHCH

O

/

Polyvinyl pyrrolidone is manufactured as a polymer from A^-vinylpyrrolidone using a hydrogen peroxide catalyst. It dissolves easily in water to form a viscous liquid, and it is also soluble in alcohol, glycerin, and ethyl acetate. It is used in hair-care products due to its film forming properties and close affinity for hair, as well as in shampoos to stabilize the lather and give luster to hair.

5.4.2.3. Nitro cellulose Nitro cellulose is an ester of cellulose nitrate; it is soluble in acetates and ketones, etc., and has good phase solubility with other resins. It forms hard films so it is used as a film former for nail enamel.

5.4.2.4. Silicone gum

CH3 I

CHa-Si-O I

CH3

CH3 I

- S i - 0 I

CH3

CH3 I

-Si-CH3 I

CH3

n = 5,000—8,000


Silicone gum is a high-molecular weight straight-chain dimethyl polysiloxane forming a smooth rubbery gum. It is soluble in volatile oils such as isoparaffin and low molecular weight silicone oils and is used in hair care products to coat split hair; after the solvent oil has evaporated a thin film repairs and protects the split hair.

5.5. Ultraviolet absorbents

The surface of the earth is continually bombarded with ultraviolet (UV) rays in the wavelengths from 290^00 nm. Ultraviolet absorbents in cosmetics are used to absorb UV light over the entire wavelength band of 290-400 nm to prevent skin damage^^^ including skin erythema, sunburn, suntan, and premature aging^^\ as well as deterioration of the cosmetic itself and the container, such as pigment color changes, breakdown of base materials, quality changes and weakening of the container.

The important requirements of UV absorbents used in cosmetics are: (1) non-toxic, with high safety and causing no skin damage; (2) high UV absorbance over a wide range of wavelengths; (3) no breakdown due to UV light and heat; and (4) good compatibility with cosmetic base materials.

The main UV absorbents used in cosmetics at present are, based on the chemical structure, benzophenone derivatives, para-amino benzoic acid derivatives, para-methoxycinnamic acid derivatives, salicylic acid derivatives, etc. Table 5.5 lists the main agents with their chemical formulae and maximum wavelength absorbance (>lmax) ^ - Fig-5.2 also shows the absorption spectrum of some typical UV absorbents^^^

Although it is possible to assess the effectiveness of UV absorbents by measuring their UV transmission or absorbance at a fixed concentration in an appropriate medium, since the absorption and absorption position changes with the type of solvent, etc., it is very difficult to evaluate the effectiveness accurately. At present, the most commonly-used method for measuring the UV absorption efficiency is to measure the actual human sun protection factor (SPF) (refer to Part II Chapter 5) 3).

5.6. Antioxidants

Cosmetics are composed of fats, oils, waxes as well as surfactants and perfumes, etc.; some of these compounds contain unsaturated bonds. In particular, it is presumed that fats and oils with two or more unsaturated bonds are easily oxidized. In cosmetics, this reaction produces compounds with bad smells or causes safety problems such as skin irritation. To prevent these changes in quality, it is necessary to add antioxidants to cosmetics to control this oxidation reaction.

Oxidation mechanisms are classified into two types: auto-oxidation, and non-radical oxidation. Auto-oxidation proceeds in the presence of oxygen via a radical-chain mechanism. Non-radical oxidation proceeds in the presence of ozone, single oxygen, etc.

5.6.1, Auto-oxidation mechanism

Auto-oxidation is a radical chain reaction occurring due to the presence of 20% oxygen


Table 5.5. Main ultraviolet absorbents

UV Absorbent (Chemical Name)

Benzophenon derivatives (1) 2-Hydroxy-4-methoxybenzophenone

(2) 2-Hydroxy-4-methoxybezonphenone

-5-sulfonic acid (3) Sodium 2-hydroxy-4-methoxybezon-

phenone-5-sulfonate (4) Dihydroxy-dimethoxybenzophenone

(5) Sodium dihydroxy-dimethoxybenzo-phenone sulfonate

(6) 2,4-Dihydroxybenzophenone

(7) Tetrahydoxybenzophenone

Para-aminobenzoate derivatives (8) Para-aminobenzoic acid(PABA)

(9) Para-aminobenzoate

(10) Glyceryl para-aminobenzoate

(11) Amyl para-dimethylaminobenzoate

(12) Octyl para-dimethylaminobenzoate

Methoxycinnamic acid derivatives (13) Ethyl para-methoxycinnamate

(14) Isopropyl para-methoxycinnamate

(15) Octyl para-methoxycinnamate

(16) 2-Ethoxyethyl para -methoxyc in

namate

(17) Sodium para-methoxycinnamate

(18) Potassium para-methoxycinnamate (19) Di-para-methoxycinnamoyl-mono-2

-ethylhexanoyl glycerol

Salicylic acid derivatives (20) Octyl salicylate (21) Phenyl salicylate (22) Homomenthyl salicilate (23) Dipropylene glycol salicylate (24) Ethylene glycol salicylate (25) Myrystil salicylate (26) Methyl salicylate

Other

(27) Urocanic acid

(28) Ethyl urocanate

(29) 4-t-Butyl-4'-methoxydibenzoylmeth-ane(Parsol A)

(30) 2- (2'-Hydroxy-5-methylphenyl) ben-zotriazole

(31) Methyl anthranylate

Structure

<P)^COH(P>-OCH3

HO

''^ SO3H

(Q^co^0^ocu, HO

(2)

H^N-^O^-CO^H

(8)

CH3

/N~KQ>~CO, - CH, - CH - (CHJsCHs CH3 ^— 1

(12) CH2CH3

CH3 0 - x O ) ^ C H = CH-C02-CH3CH(CH2)3CH3

(15) CH2CH3

CH20CO-CH(CH2)3CH3

C H 3 0 - / P ^ C H = CH-C02CH ' ru vrrv 1 Url2Url3

C H 3 0 - ( Q ) - C H - C H - C 0 2 C H 2

(19)

corl'"' ©rj dcH3

(22)

CH3

1 ^ = ^ II II ^ ^ CH3 0 0

(29)

CH3

a:>^ HO

(30)

(Imax)

288,325

285,320

288

310

312

312

308

358

298,340

(Society of Japan Pharmacopoeia : The Japanese Standards of Cosmetic Ingredients, 2nd Edition, Yakujinippo-sha, 1984) (Japan Cosmetic Industry Association : Japan Cosmetic Ingredients Dictionary, 2nd Edition, Yakujinipposha, 1989)


<

320 340

Wavelength (nm)

Fig. 5.2. Absorption spectra of ultraviolet absorbents (Y. Takase, M. Ishihara, K. Toda, F. Morikawa eds: aging and Skin, Seichi Shoin, 1986).

in the air and it is the most important reaction to be noted to prevent the oxidation of cosmetics. Auto-oxidation response is accelerated or inhibited by many factors including heat, light (UV), metal ions (especially, iron and copper), water, proteins, etc.

The following equations shows the main reactions of the auto-oxidation mechanism.

Initiation of chain reaction

Chain transfer reaction

Termination of chain reaction

RII

R O O H

R O O H

R •

R O . •

RO •

R •

R •

R O , •

+ M ' "

+ 0 .

+ R H

+ R H

+ R •

+ R O , •

+ R O , •

- ^ ^ - ^ "-"> —>

^

R •

R O -

R O •

R O , •

R O O H

R O H

RR

ROOR

ROOR

+ • O H + ]Vi('Hi)+^ O H

+ R • + R •

( 1 ) ( 2 )

( 3 )

( 4 )

( 5 )

( 6 )

( 7 )

( 8 )

( 9 )

The auto-oxidation reaction is a chain reaction, so lipid peroxides accumulate rapidly. If lipid peroxide is present initially or accumulates by the progress of auto-oxidation, as shown by equation (5), the radical chain reaction can be initiated again, as shown by equations (2) and (3)3435).

5.6,2, Prevention of oxidation

To prevent the auto-oxidation reaction, it is necessary to suppress the initiation and chain transfer reaction phases. Reactions (1) and (2) can be suppressed by storage in a cool


location and by use of UV absorbents. In addition, since lipid peroxides are a source of radicals, peroxides should be decomposed by a non-radical mechanism. Chelating agents are useful in suppressing reaction (3); in addition, oxygen accelerates the radical chain reaction so it should be eliminated.

In addition to preventing generation of radicals, reactions (4), (5) and (6) should be suppressed by scavenging generated radicals as quickly as possible, thereby breaking the chain reaction. Compounds able to perform these functions are called chain-breaking antioxidants and some are listed below: - tocopherols

BHT (dibutylhydroxytoluene) - BHA (butylhydroxyanisol) - gallic acid esters - NDGA (nordihydroguaiaretic acid), etc.

These antioxidants may be used singly or in mixtures where they often have a synergistic effect. Such materials are often also marketed as mixtures of antioxidants and other compounds promoting the antioxidative effect.

Typical antioxidant promoters are phosphoric acid, citric acid, ascorbic acid, maleic acid, malonic acid, succinic acid, fumaric acid, cephalins, metaphosphate, phytic acid, EDTA, etc.

When using antioxidants and antioxidant promoters in cosmetics, attention must be paid to irritation, toxicity, and color changes; in addition, they must be dissolved in an oil-water system. It is also necessary to contribute to antioxidation in the system.

5.6.3. Confirmation of efficacy of antioxidants

The efficacy of antioxidants is expressed as the ease with which the antioxidant itself is oxidized, or in other words, how easily hydrogen is eliminated, using the redox potential.

For the application of antioxidants to cosmetics, some experiments are necessary to determine the kind and amount of antioxidants. There are a number of methods including the AOM (active oxygen method), the Schaal oven test, the oxygen absorption method, the UV irradiation method, and the heating method. All of these are performed under accelerated conditions, so in actual use, it is preferred to perform a comparison using preservation tests to confirm whether or not the results of the accelerated tests are in line with actual results.

In addition to selecting the appropriate type and amount of antioxidant to prevent oxidation and maintain the cosmetic quality, it is important to choose high-quality raw materials for cosmetics that do not include impurities which might promote oxidation, as well as to establish appropriate manufacturing methods, and to prevent inclusion of metal ions and other oxidation promoters.

Recently, lipid peroxidation has received much attention in connection with its pathological effect and possible contibution to aging, cancer and other diseases^^^ In other words, antioxidants may not just prevent the oxidation of cosmetics, they can play an important role in preventing oxidative reactions in the skin thereby preventing damage caused by UV radiation and aging.


5.7. Sequestering agents

When metallic ions are mixed with cosmetics, they can directly or indirectly lower the quality. Metallic ions can cause changes in perfume and color and can also promote oxidation of oily raw materials. In addition, they can block the action of pharmaceutical agents and can cause transparency to be lost through precipitation, for lotions, etc.

Compounds used to deactivate these metallic ions are called sequestering agents. Some typical sequestering agents for metallic ions are listed below but the most generally used is the sodium salt of EDTA: (1) sodium edetate (EDTA) (2) phosphoric acid (3) citric acid (4) ascorbic acid (5) succinic acid (6) gluconic acid (7) sodium polyphosphate (8) sodium metaphosphate

5.8. Other raw materials

In addition to the previously described components of cosmetics, there are a number of liquids such as ethanol used in liquid hair setting hair care products and hair tonics, and ethyl acetate used as a solvent for the resins used in nail enamels; there are also propel-lants used in aerosols as well as metallic soaps used for the purpose of dispersing pigments. This last section only deals with metallic soaps.

5.8.L Metallic soaps

Metallic soaps are defined as soaps containing a metal salt of a higher fatty acid; the most common are the alkali metal salts such as sodium and potassium of higher fatty acids. Other non alkali metal salts include calcium, zinc, magnesium, and aluminum, etc.. Metallic soaps are obtained by double decomposition of alkali metal salts of higher fatty acids and metal salts such as zinc sulfate, or by direct mixing of metal oxides and hydroxides with higher fatty acids. They are insoluble or only slightly soluble in water.

Metallic soaps have different properties depending on the structure of the fatty acid and type of metal ion but they have various functions, such as improving the dis-persability of pigments, as well as improving the viscosity of lipid materials by gelation and increasing the smoothness on the skin and the adhesion. Zinc stearate is used in face powders and baby powders to improve the smoothness and feeling on use.

Aluminum stearate is used to increase the viscosity of liquid paraffins, while magnesium stearate is used to improve pigment dispersion^^^


References

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