COSMETICS VERSUS TOPICAL THERAPEUTIC AGENTS BY IRVIN H. BLANK, PH.D. * Presented December ¾, I962, Symposium on Cosmetic .4spects of Dermatology, co-sponsored by the Committee on Cosmetics of the .4merican Medical /lssocialion and .4merican ,4cademy of Dermatology ABSTRACT There is a similarity in the composition of some types of cosmetics and topical therapeutic agents. Although the purposes for which comparable groups of products are used may not always be the same, their mechanism of action and their efficacy are frequently similar. The close relationship between some classes of cosmetics and topical therapeutic agents is discussed. No longer is there a sharp dividing line between the interests of cosmetic chemists and dermatologists both groups are working to devise ways of improving the condition and function of skin, hair and nails. The area of common interest is steadily expanding, but the objectives of these two groups are not identical. The dermatologist's primary interest is alleviation of existing or threatening pathology of immediate or potential severity, while the cosmetic chemist's primary interest is protection, improvement and minor alteration of relatively normal tissues. In recent years, cosmetic chemists have done more than design prepara- tions which counteract the symptoms of simple dryness and cover blemishes in the skin they have also begun to add biologically active substances to their preparations and have thus made them somewhat analogous to cer- tain pharmaceutical products. Consequently, it has become important to consider how certain types of cosmetic and pharmaceutical products resemble and differ from one another. No attempt will be made here to analyze specific products. The following categories of products will be discussed with emphasis upon their mechanisms of action: emollients, keratolytic agents, cleansers, antimicrobial preparations, antiseborrheic agents, antiperspirants and sun screens. * Research Laboratories, Dept. Dermatology, Harvard Medical School, at the Mass. General Hospital, Boston 14, Mass. 433

434 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I. Emollients Emollients are used to counteract symptoms of dryness: (a) roughness of the cutaneous surface, and (b) decreased flexibility of the stratum cor- neum. They surely constitute one of the largest categories of cosmetic agents and include cold creams, lubricating creams, vanishing creams, bath oils and hand and body lotions. Dermatologists use similar preparations but usually refer to them all as emollients or protective agents and avoid the subgrouping found among cosmetics. Although emollients may occasionally consist of a single oily substance, such as petrolatum, they are now usually composed of oil, water and an emulsifying agent. Bath oils, as marketed, seldom contain water more frequently they contain a natural oil which has been chemically altered or mixed with an emulsifying agent, with the result that when used by the consumer they readily form an oil-in-water emulsion when added to water. That water is a much better plasticizer of cornified epithelium than any oil is now well known and generally accepted (1). It is not necessary to review the background of this observation, but mention should be made of several misunderstandings which have arisen since this concept was intro- duced. First, one should not conclude that the emollient action of an emulsion is necessarily better than that of an anhydrous oil simply because the emulsion contains water which might hydrate the stratum comeurn. When an oil-in-water or a water-in-oil emulsion is spread on the skin, the small amount of water present can make only a minor contribution to the total prolonged emollient effect of the emulsion, because it soon evaporates. Water, alone, almost immediately relieves a sensation of dryness, but this relief is short-lived if the water is allowed to evaporate. When an occlusive film of anhydrous oil is placed on the cutaneous surface, the stratum comeurn becomes hydrated by water which diffuses outward from the underlying tissues. Theoretically at least, an anhydrous oil might serve as a better emollient than an emulsion because the directly applied oil might be more occlusive than the oily film deposited from the emulsion and thus keep the stratum comeurn hydrated for a longer time. Second, retention of water by the stratum comeurn is not the only mechanism by which an oily film exerts its emollient action. The oil is a "lubricant" and makes a rough cutaneous surface feel smooth. Third, the naturally occurring film of oil on the cutaneous surface (sebum) is poorly occlusive and probably does not play a major role in retention of water by the stratum comeurn. When there is a deficiency of sebum on the skin, either for natural reasons or because of removal by detergents or organic solvents, one might expect the skin to be rough and therefore it would seem dry because of this roughness and not because of any decrease in the flexibility of the stratum comeurn.