350 JOURNAL OF THE SOCIETY OF COSMETICS CHEMISTS preclude alkalinity, per se, as the cause of irritation from surface- active agents. Blank (18) has stated that neither the alkali nor the fatty acid alone is the cause of soap dermatitis he believes each is a factor. According to Mumford, the organic sulfonates and sulfuric acid esters appear to remove nat- ural fat from the skin and may therefore act as irritants. Duem- ling's work (7) indicates surface- active agents may possess the ability to penetrate the skin, per- haps indirectly, which Lane and Blank (14) suggest as a possible cause 'of cutaneous irritation. These and many other dermatological studies indicate the possibility of ionic character being related to skin irritant action. Patch tests (8) on the surface- active agent alone, or on aqueous dispersions of the agent, serve only as a guide to safety. In most cos- metic products the surface-active agent is only a minor ingredient. In shampoos the synthetic detergent may be the major ingredient. Shampoos, however, are seldom used daily and are thoroughly rinsed away after use. So the conditions of usage as well as the concentration must be considered. Furthermore, there is evidence in the literature (15) that skin irritation levels of a given agent depend on more factors than time and concentration for example, a 3 per cent aqueous solu- tion may be non-irritating though 3 per cent in a fatty cream or oint- ment may cause irritation. EVALUATION Assuming it is safe to consider usage in a cosmetic product, what other tests are apt to be helpful in the choice of proper surface-active agent? Consideration of a few pub- licized methods may be of help. The well-known Drayes Test, de- •veloped for the textile industry, indicates how rapidly an aqueous dispersion of a synthetic will wet textile fabric under standard con- ditions. The good penetrating wet- ters can be compared by the test, but not the surface wetters. Some of the non-ionics lower the surface tension of the water to a greater de- gree than may anionic or cationic agents, but the nQn-ionics generally have poor Drayes Test results. Personally I believe there may be some connection between Drayes .:, Test effects and penetrating ability on human skin, but it is difficult to prove. Surface tension and interfacial tension lowering effects may measured, and are generally re, ported in the manufacturer's litera-. i ture. Ability to lower interfacial :: tension is undoubtedly tied up with :71 emulsifying ability. The Spread'.::?:: ing Coefficient, which is mathemat-.:: . ically derived from surface and terfacial tension measurements seems to be a means of distinguish::11' : ing to some degree between pene-? trating and surface wetting agents. :il It ought to have value to the metic chemist, perhaps even more i! than the Drayes Test. The developmen t o f "water n

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