24: JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the original patch test. We owe a great debt to our next speaker, Dr. Louis Schwartz, who is the out- standing authority on this subject, and in whose presence I hesitate even to mentior• patch tests. His publications and written advice have been of inestimable value to us, and before tackling any unusual problem, we always ask ourselves, "How would Louis Schwartz do it ?" Some substances, particularly cer- tain dyes, may not be either primary irritants or sensitizers, but they may be so-called photosensitizers, that is they may cause a reaction only when activated by ultra-violet light. Thus any pigmented cosmetic to be used on the face or hands and which may be exposed to the action of sun- light during use, such as lipstick, rouge, face powder, cake make-up, nail lacquer, etc., should be tested forphotosensitization. This is done by exposing the patched area to the action of ultra-violet light for a period of time calculated to produce a mild erythema on the subject. This varies from five to fifteen min- utes, depending on the complexion of the subject. It is preferable to use natural sunlight, but because it is impossible to standardize, we always use artificial ultra-violet light. We use a 1 per cent solution of' eosin as a positive control, and we find that anywhere from 10 to 25 per cent of the subjects are photo- sensitive to eosin. We must bear in mind that the results of patch tests are much more dependable when they are positive than when they are negative. In other words it is much easier to say that a product should not be used because of positive reactions, than it is to say it is probably safe to use because of n. egative reactions. All products passing the patch test should be followed up by actual use tests before the product is placed on the market. 'So much for safety • tests. Now let us turn our attention to perform- ance tests. There are no set rules to go by, but we must adapt our tests to the •product and what is ex- pected of it. Stability tests are of prime importance. The product should not change its characteristics on aging for a reasonable period of time. If it is a cream, it should re- main as a cream and not harden or cake. If it is an emulsion, it should not break into two phases. Acceler- ated aging tests are run at 52øC. (about 125øF.) when. the product will stand that temperature. In general, we have found that if a product is stable for three weeks at 52øC., it will probably be stable for one year of normal shelf life. Sta- bility at low temperatures is also a factor. These tests are run at 4øC. (about 40øF.). It is often advis- able to determine whether a product that has been frozen will regain its original consistency on thawing. Comparative accelerated aging tests are also run on emulsions in a cen- trifuge, where different competitive products are centrifuged at a defi- nite speed and the time required for each emulsion to break is deter- mined. Stability to bacterial and fungous

EVALUATION OF EFFICACY AND SAFETY OF COSMETICS 25 decomposition is an important fac- tor, particularly for creams. Is the product actually bacteriostatic and fungistatic? Will it inhibit the growth of typical bacteria and fungi under optimum conditions for their growth? Failing that, will these organisms grow in the product itself if it is inoculated with them? Many headaches due to mold growth and rancidity in jars could have been prevented if these relatively simple tests had been run. We have had liquid products that were perfectly stable as long as the bottle was un- opened, but that soon developed a foul odor on opening and partially removing the contents, due to aerobic, air-borne organisms which would only grow when air was admitted. Pigmented cosmetics are tested for their relative opacity and cover- ing power. Nail polishes and lac- quers are tested for their light re- flectance and for their drying time, adhesion to metal and other sur- faces, and for flexibility of the dried film. Cake make-up is tested for its adhesion to leather, simulating skin, and for its ease of removal by soap and water as well as by cleans- ing creams. Many other tests are devised as a method of evaluating the comparative performance of various products. Sun-tan lotions, although legally drugs, are more often thought of as cosmetics. Their effectiveness de- pends on their ability to absorb the erythema-producing ultra-violet waves of sunlight, in the band be- tween 2900 and 3200 Angstrom units. It is only the rays within these wave-lengths that produce sunburn and which should be screened out. Since these same wave-lengths are the ones that pro- duce tanning, it is not desirable to exclude them entirely, but only to reduce them by about 75 to 90 per cent. Ultra-violet absorption curves are run on these products, in a quartz cell in a film thickness of 0.02 ram., which is the usual thickness of the film on the skin. Some sun-screen- ing agents may be very effective in absorbing ultra-violet rays, but may be totally unfit for use in a sunburn preventive, because they are rapidly destroyed by the longer wave- lengths in sunlight and would rapidly lose their effectiveness on the beach. For this reason, the ultra- violet absorption curve is again run after exposing the product in the quartz cell to the action of four hours of sunlight. These tests are comparative and must all be run simultaneously. Results obtained on one day cannot be compared with those obtained on another day. Deodorants and antiperspirants are other products which we usually think of as cosmetics, although anti- perspirants are actually drugs. A deodorant which merely masks the odor of perspiration with a more pleasant odor is difficult to test. This can be done by use of the osmo- scope, which is an instrument that utilizes the principle of diluting a given concentration of odor with air until a concentration is reached where the objectionable odor is