318 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS lators feel it "self-evident" that such soothing ingredients must also act as anti-irritants if applied to the skin in conjunction with known irritants. Unfortunately, this self-evident assumption is not always justified. In recent years it has been learned that safety is a relative matter. No material is absolutely safe to use on the skin unrestrictedly, nor does anything exist which is always unsafe. Materials which are known to be soothing to irritated skin will not always act as anti-irritants when mixed with inflammatory or otherwise irritating agents. The purpose of this paper therefore is not to establish absolutes nor to provide lists of ingredients guaranteed to make products safe. Instead, the purpose is to show that the skin and eye irritation potential of various cosmetic ingredients can vary greatly, dependira', on •heir "en- vironment" (i.e., other components of the formulation), and on the mzthod of use and bodily area to which thefinished formulation is applied. A corollary of this argument is the inescapable conclusion that "positive" (safe) and "negative" (unsafe) lists of cosmetic ingredients, such as have been suggested in several European countries as "guides" or as devices for regulating the activities of cosmetic manufacturers, have no sound scientific basis. There is no question that the irritative properties of many ingredients can be altered drastically by suitable compounding techniques. Therefore, it must also be evident that the irritation potential of a cosmetic cannot be determined solely on the basis of the known irritative properties of each of its individual com- ponents. The irritation characteristics of components are no additive. They often exhibit a synergism, either positive or negative, which appears at random and is unpredictable. These synergistic effects are the basis of several recent patents (1-3) concerned with anti-irritant combinations. It would not be wise, therefore, to draw generalizations from the anti-irritant effects noted in this paper. Some agents may be useful only in the specific formulations which were tested. It will also be shown later that some materials can act as anti-irritants in one type of formula and then reverse their roles and increase the irritation potential of a different type of product. GENERAL BACKGROUND Cosmetic chemists must beware the temptations of two sirens, medicine and cosmetology, who stand on opposite shores of the nar- rows through which they sail, waiting to seduce and destroy those who

USE OF ANTI-IRRiTANTS IN COSMETIC FORMULATING 319 draw too near. Formulators must not be tempted to practice healing, and (except for testiug purposes• their business is not primarily the art of applying cosmetics to the hmnan integument. Their proper concern is the preparation of products which are both efficacious and safe to USe. Unfortunately it is sometimes difficult. to prepare prcducts which have both of these properties. By definition, topical preparations which produce more than mere cosmetic effects are said to "have activity." This activity often results from their ability to react with that portion of the body to which they are applied. Both in theory and in fact, therefore, the more "active" a product the greater is the likelihood that it may be either a primary irritant or a skin sensitizer. Although long experience may eventually prove an ingredient per- fectly safe, the cosmetic chemist may be somewhat concerned the first time he tries it. Many formulators therefore routinely include "soothing" ingredients in vehicles intended as carriers for such active agents, in order to forestall possible primary skin or eye irritatiop. Their premise is reasonable. They assume that a material which is itself soothing to irritated skin will also act as an anti-irritant when combined with such active ingredients. Often, however, inexperienced workers use such anti-irritants without checking two factors: (a) Does it actually reduce irritation, measurably and substantially ? (b) Does it function without unduly reducing the efficacy of the active ingredient ? Unless a proposed anti-irritant fulfills both of these conditions, there is no point to using it. It would be more logical simply to reduce the total quantity of active ingredient in the formula. Many workers are convinced that inclusion of protective colloids is helpful in reducing the irritation potential of certain types of cosmetic formulas. Others feel that aqueous solutions of irritants are rendered less irritating by emulsifying them with oils. Finally, some believe that it is possible to "complex" certain irritants in such a way that they still retain their useful properties, yet are no longer irritating. Each of these beliefs can be dramatically justified in certain special cases. No one questions the fact that certain bases are "safer" than others when used as vehicles for applying irritants to the skin. Un- fortunately, however, although extravagant claims are made for many ingredients, rigorous proof of anti-irritant activity is almost nonexistent today in the literature.