CUTANEOUS REACTIONS TO ALLERGENS AND IRRITANTS 249 •/4-inch square piece of white linen. lfit is a powder it is moistened with water if it is a solution the piece of linen can be soaked in it. The small patch is placed on the normal, intact skin of the inner surface of the arm or on the upper back and covered with a larger piece of oiled silk or other impermeable tissue. This is then covered and held in place by a strip of adhesive plaster. The patch is allowed to remain for twenty-four to forty-eight hours and the reaction noted on removal. This is called the closed patch test. The positivity of the test is read as 1, 2, 3, or 4 plus, depending on the degree of reaction. The test site should be observed again for possible delayed reactions one, two, and three days after removal of the patch. It must be remembered that a negative patch test does not neces- sarily rule out the suspected sub- stance as the cause of the dermatitis. The patch is usually not placed on the area of the skin that is inflamed and the site of the test may not be sensitive to the allergen at the time the test is performed. An exam- ple of this fact is seen in nail polish dermatitis. Usually the eruption appears on the eyelids and lower cheeks, but the test is not done in these areas. It is placed on the neck, arm or upper back and these sites may not be sensitive and may not react. One must also consider whether the test was done with the exact causative substance. In a dermatitis from a "cold wave" permanent, the reaction is generally due to varying degrees of primary irritation, rarely to hypersensitivity to the ammonium thioglycolate so- lution itself. In other words the dermatitis may not have been caused by the cold wave solution but was due to irritation from the combina- tion of the acid, the softener, and the fixative. A patch test with the ammonium thioglycolate, in the concentration that is ordinarily used, might and usually is negative, but tests with the other substances or a combination of them would probably be positive. It should be remembered that the patch test often does not simulate the manner in which the cosmetic is actually used, and that the length of expo- sure, friction, sunlight, and other factors may contribute to the sensi- tivity but are not duplicated in the test. On the other hand a positive patch test with substances that are primary irritants does not necessar- ily prove they are the cause of the dermatitis or that the dermatitis is due to hypersensitivity. For example, it is not good procedure to do routine closed patch tests with soap, antiperspirants, depilatories, or other primary irritants. They would give positive reactions in twenty-four to forty-eight hours in a large percentage of people. This also occurs in patch testing with some creams and other preparations which contain volatile ingredients that are primary irritants in certair•. concentrations. As cosmetics are usually not covered when used, a large part of these volatile ingredi-

250 JOURNAL OF THE SOCIETY ents evaporate and in that level of concentration the product is not an irritant. However the closed patch test does not allow this evaporation and the cosmetic which is harmless in actual use may give a positive reaction with the covered test. For this reason the "usage tests" are em- ployed to check and interpret the reactions obtained in patch tests with certain chemical substances. In trying to ascertain whether a cosmetic is the cause of a dermatitis it is at times better to apply the preparation daily to the same site of skin for a week in the same manner in which it is actually used. That will check on the closed patch test and determine the skin sensitizing and/or skin irritating properties of the particular cosmetic. Besides its use to discover the specific cause of a dermatitis, the patch test is of great importance as a means of determining the possible danger of a preparation that is to be sold to the public. Before a new product is put on the market, the so-called' "prophetic patch tests" should be done. In this procedure routine patch tests are performed on at least 200 subjects. The prep- aration is left on for twenty-four hours and reactions are noted that day and also twenty-four, forty- eight, and seventy-two hours after removal. Two weeks after the first tests were applied, the closed patch tests are repeated on the same sub- jects, allowed 'to remain for forty eight-hours, and the reactions are again read each day for three days after removal. The first series of OF COSMETIC CHEMISTS tests will indicate whether the cos- metic is a primary irritant. The second series will show its sensi- tizing properties. If there are no positive reactions in both series, it is usually safe to place the product on trial sale. However, again it must be remembered the pre-use patch test will not always avoid the possible occurrence of an allergic dermatitis in some persons. For that reason it is safest to also do the usage test besides the patch tests on the same 200 subjects. The product is applied daily for four weeks in the same area and in a similar manner as it would ordinarily be used. If no cases of dermatitis result, the product may then be put on sale. Even if all the tests are negative that does not mean an individual may not become sensitized after using the product for a variable length of time. Sometimes that question can only be answered after a sufficient trial by many persons over a long period of time. In the competition of cosmetic manufacturers to outdo each other in their search for new products and changes and possible improvements in their old products, the incidence of dermatitis' is bound to increase. However the cosmetic chemist can do a great deal to prevent or reduce this to a minimum. He should know the possible effects 'of the chemicals he intends to use in these preparations and he should be aware of theiF potentiality to sensi- tize and irritate the skin. With the help of the dermatologist he can be of service not only to 'the