324 JOURNAL OF THE SOCIETY OF COSME'•IC CHEMISTS This paper is to call your atten- tion, when testing cosmetics, to the use of appropriate common-sense modifications of the original covered prophetic patch test which was de- vised for testing fabrics. EXPERIENCES WITH AND CONSIDERATIONS OF THE HUMAN PATCH TEST METHOD* By HERMAN A. SHELANSKI, P•.D. Industrial Toxicology Laboratories, Philadelphia ¾, Pa. SINCE PRE-HISTORIC times mankind has attempted various methods of improving their ap- pearance to make themselves more attractive. Thus tattoos, war paint, and cosmetics have been used in sundry cultures at different periods of time. Today, the manufacture of materials which come in contact with the skin includes many im- portant industries. These indus- tries owe their existence not only to the demand for their products or the improvement brought about by their products but also to the fact that these products are in- nocuous when they are applied to the human skin. It is self-evident that no matter how beautiful a certain preparation may make a woman, if this product causes illness, the demand for it would cease to exist. Therefore, it is necessary to as- certain if these products are in- nocuous before they are put on the market. The most logical method of obtaining conclusive proof is to test a substance on human skin. This is * Presented at the December 5, 1950, Meet- ing, New York City. the so-called skin patch test which has become so important in recent years, especially with the new F.D.A. regulations. However, even before human be- ings can be exposed to.any new sub- stance it is wise to investigate the substance's toxicity on animals. In this way, any substance with marked toxicity can be eliminated from general use before humans are tested. Without going into detail of these preliminary studies, suffice it to say that several species of animals should be used, the material tested not only on the skin but also on the conjunctiva of the eye. Once a new substance has suc- cessfully passed the preliminary tests on animals, the final test may be performed, namely patch test- ing on a series of human subjects. Although the human skin patch test had been used for many years, it was largely through the efforts of Dr. Louis Schwartz, Retired Chief of the Division of Dermatoses, United States Health Service, that the human patch test was developed

EXPERIENCES WITH HUMAN PATCH TEST METHOD 325 as a standard basic technique in de- termining the effect of a substance upon the skin. In brief, this basic technique consists of: 1. Application of the substance directly to the skin for a defi- nite period of time. 2. Removal of the substance from the skin. 3. A recuperation period of a definite length of time. 4. Reapplication of the sub- stance directly in contact to the skin of the same subject. 5. Removal of the second appli- cation. The technique of this basic method may be modified depending upon circumstances, that is, the nature of the material to be tested--its volatility, solubility, pH, and os- motic pressure, to name but a few. The substance is placed in contact with the skin by means of a patch. The material used for the patch must be one which is inert in regard to the skin. For this purpose many investigators use sterile cotton gauze pads or lintine discs. If the sub- stance to be tested is a solid, a meas- ured amount is placed on the disc and spread uniformly over the en- tire surface. If the substance is a liquid, the disc is saturated with the substance. This disc is then placed directly in contact with the cleansed skin of the human subject. The disc is then covered with a water- proof film such as cellophane or waxed paper. It is important that the film of cellophane or waxed paper cover an area larger than that of the disc. This is done so that the adhesive tape used to kee p the disc in place does not come in con- tact with the disc itself or the skin immediately surrounding the disc, so as to leave a definite margin of skin between that which is exposed to the substance and that which is exposed to the tape. That is im- portant because many of the adhe- sive materials used in tapes produce skin reactions by themselves. Fundamentally, the substances coming in contact with the skin may be divided into two types, namely, primaryirritants and second- ary irritants. A primary irritant is a substance which produces irri- tating effect on the skin on first contact. A secondary irritant is a substance which produces irri- tation of the skin only after the skin has previously been exposed to the substance. The fact that there are both primary and secondary irritants serves as the rationale behind the method of the patch test as outlined above. The patch test procedure is planned to detect both types of irritants. A primary irri- tant may be detected at the second step of the procedure as outlined above, that is, when the first appli- cation is removed from the skin and the results determined. A sec- ondary irritant is detected at the fifth step of the patch test procedure. The mechanism of irritation is radically different. The primary irritant produces its effect by virtue of the inherent irritating qualities of the substance. This is a non- specific type of irritation, the effect is similar to that caused by heat, low pH, rapid volatilization, or