SURFACE-ACTIVE AGENTS IN COSMETICS 351 ..ber as a method of evaluating ab- ': sorption bases and emulsifiers has i .ii:,i been discussed by &Navarre (5). A i : recent paper presented by W. C. ? 'i Griffin detailed some refinements in !•.'::': techniques of measurement. ..,.,.:•? The solubility characteristics of iii'?i.: the agent, while an inherent prop- :i •i: .i :' erty, afford a means of choice be- !i!-:•: tween various agents for such jobs •': :': as emulsifying, solubilizing, etc. i•i'i!ii iWar-time government studies on 7:1:i:', '.,mulsifiers for kerosene and other .•i?" olvents showed that an agent would :'•.: . not give stable emulsions unless it ,?'::-' was reasonably soluble in the sol- i:•::i': vent. No fully sulfonated product :il : i.was soluble in, or would emulsify, ':: '.i!::kerosene only the non-ionics were (:i'i•:'satisfactory emulsifiers, and only certain of them. m P P LI CATI O N S Detailed discussion of applica- ß ':i:' trans and properties of surface- •:)'active agents is too lengthy for the i!511 purpose of this article, but certain properties and needs can serve as guideposts, deNavarre (5) has di- vided cosmetic products in to creams, lotions, powders, make-up, soap, and miscellaneous. Similarly sur- hce-acti•e agents can be grouped by their primary functions as wet- ting agents, detergents, emulsifiers, solubilizers, dispersing agents, and miscellaneous. For creams and lotions, which are mainly mixtures of oils and water, emulsifiers are of primary impor- tance. Most surface-active agents have some emulsifying ability, but in general a product is primarily a wetting agent or primarily a de- tergent, or excels in some one spe- cific field. The best emulsifiers for cosmetic oil-and-water systems are generally not the top notch de- tergents or penerrants and vice Lack of solubility in the oil phase, even in the presence of water, seems to eliminate most of the commercial alkyl aryl sulfonate types, and vir- tually 'all commercial products con- taining salts, as primary cosmetic emulsifiers. Most anionic and cat- ionic agents are not acceptable as sole emulsifiers for one or more reasons, including solubility char- acteristics, possible skin irritation factors, inability to give easily pre- pared emulsions of long stability, color, odor, etc. The non-ionics are free from most of these objections, so the problem is to pick the one that most nearly fits the requirements of a specific formulation.. An emulsifier that is primarily oil-soluble tends to produce water- in-oil emulsions. A water-soluble surface-active agent will produce oil-in-water type emulsions. This rule of Bancroft seems to hold pretty well for simple emulsions with one emulsifier. Sometimes, of course, it seems that technique of preparation is even more important (13). And synergistic effects, or the use of stabilizing emulsifiers that may or may not have similar solu- bility characteristics, are often used to increase or decrease emulsion stability. The use of thickening agents, such as certain stearate es- ters or natural gums, which may or

352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS may not be surface active, is often a technique for improving emulsion stability by mechanical means. The use of two or more surface- active agents in one formula, to accomplish the synergistic effects just mentioned, can perhaps be considered a trend. While ex- perience has proved synergistic ef- fects must occur in certain empiri- cally devised formulas, it seems that only recently has there been any recognition of the possibility of a scientific basis for such combina- tions. Prediction is still difficult the combination may possess the desired properties of both agents, or the undesired ones, or the good may cancel out the bad. Obviously anionic and cationic agents should not be used together, but there are many examples of combinations of agents that are compatible. Thus in formulating a liquid bubble bath, it has been found advantageous to use an alkyl aryl sulfonate or a fatty alcohol sulfate with fatty amides. The use of a small amount of W/O emulsifier in an O/W for- mula often exerts a stabilizing ef- fect the reverse is also true, as most emulsions of good stability seem to contain small amounts of both phases. Data on interfacial tension measurements of combina- tions gave us a lead on that. C. om- binations of synthetics with soap are increasing in number, despite the almost inevitable loss of some foam- producing value. The solubilizing effect of one synthetic on another is often used to give clarity or to pro- mote stability or ease of dispersion. The ability of certain surface- active agents to dissolve essential oils, such as water-insoluble per- fume oils, and to carry the dissolved oil into an apparently clear solution in water, is an interesting property. Among these products are certain of the fatty amides and some of the polyoxyalkylated fatty acids and their esters. Use in colognes, after- shave lotions, theater sprays , and pine oil bath oils is well known. For cosmetic products requiring foaming properties, the fatty alcohol sulfates (24), the alkyl aryl sulfo- nates (10), some of the fatty amides and the amine soaps compete with normal soaps (12, 16). But where non-foaming detergency is required, as in cleansing creams and lotions, mineral oil combined with a non- ionic ester or non-foaming fatty amide emulsifier is indicated. Since the time of contact with the skin is short, the limitations of skin irrita- tion effects is less important in shampoos, bubble baths, hair wave lotions, and the like. It is obviously more important in shaving creams and products that are used under conditions involving stringent me- chanical action, even though they may be removed wi thin a few minutes. In products involving hours of con- tact, all ingredients are contributory (19). The net result is that the number of surface-active agents that can be considered for utilization in- creases as we go from emulsion cream formulation to detergent and foaming types of cosmetic items. Solid, water-free cosmetic prod- ucts such as lipstick, rouge, and face