SURFACE-ACTIVE AGENTS IN COSMETICS 349 concentrated acids, alkalis, and saline solutions. So cationice find use in marine paints and varnishes, iii}i!jii:i:•:i•::iin carbonizing wool, in certain tex- ?:!.!!ftile softeners. Their' germicidal :::•:.'•:i)•:•':?applications are well known. The agents of group D tend to act as ?:::•:• '::spreaders, or surface wetters, and are widely employed as emulsifiers. Unfortunately for any hope of suc- :•)½}:•:?:cessful classification along these •?•:.: :::' lines, no one group has a very strong monopoly on any particular set of properties. In actual practice physical and :::•::• .::.chemical combinations of two or more of these agents are often used. Thus compatibility becomes an im- P. •'•:•}::::portant hctor•one readily found ¾•.: :•:•. on testing but one not evident in usual methods of classification. One example is the use of glyceryl mono- •)'i?:•:f. stearate, a non-ionic, in emulsion creams using soap formed in situ as the major emulsifier. Combinations :•: .':'.' of two different fatty amides, or two non-ionics are also well known to everyone. The textile field, with its :.::? ::softening oils, and the war-time program of oiling woolen blankets, has shown the value of utilizing anionic or cationic agents com- blned with non-ionics to give stable emulsions that are substantive to fabrics, animal hair, and inanimate objects carrying over of these techniques to cosmetic items is on the increase. COSMETIC PKOPEKTIE8 What properties, other than those shared in common by all surface- active agents, are important to cos- metic applications? Physical form, appearance, color, odor, sometimes even taste, and cost per pound cer- tainly deserve consideration. Dif- ferences in physical properties, such as foaming ability, or physical form, or chemical stability under con- ditions of usage are naturally very important factors. Most of these properties are obvious as soon as a sample of the product and technical data are made available to the cos- roetic chemist. The requirements of specific formulations therefore en- able him to pick out a score or more possibilities out of hundreds of agents available. Dermatological aspects are of pri- mary importance (20). The prod- uct should be safe when applied to the skin under possible condition of usage. Incidently this means that even toxicity on ingestion must be considered (3, 21, 22), for children and their pets may try to eat or drink the product. There is also evidence that wetting agents may bring about penetration of the skin, if not directly perhaps through emulsification and transfer to the glands (11). A recent study by Dodd, Hart- mann and Ward (6) on surface-ac- tive agents as potential irritants in ointment bases is worthy of note. Nine surface-active agents were tested for irritant properties on rabbits and human beings. In the series only the ionic surface-active agents were irritating to human skin, while the non-ionics were non- irritating. Their data seems to

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