SKIN PATCH TEST 155 edge afforded the same status and prominence in dermatologic literature as a major advance in medical and scientific knowledge? Example HI Allergy is an acquired state of reactivity. It is manifested when specifi- cally sensitized tissue-the shock organ-is exposed t•o the allergen in question. A dose relationship exists. It is particularly characteristic for the allergic mcchanism to be activated by unusually minute amounts of the allergen. Although the foregoing statements are an oversimplification of the subject, they are basic tenets in the technic of skin patch testing. Deviation from these principles demands cautious interpretation of the test results. We are presently observing skin patch test technics that bear little or no relationship to customary usage of a consumer product (e.g., 10 times and 9,0 times use concentration of a suspected allergen, incorporation of irritating agents in the test vehicle, especially devised vehicles with unusual keratin or epidermal penetrating characteristics, and preliminary stripping of keratin). The test results from such procedures may complicate and confuse what they purport to simplify and the neomycin story illustrates it best. Current tabulations of common agents causing allergic contact type derma- titis position neomycin high on the roster. This questionable honor was be- latedly acquired because the conventional closed skin patch test with use- concentration .of neomycin failed to produce positive tests in selected patients in whom the association was suspected. However, when the test concentra- tion was increased by a factor of 10 or 20 times use, the harvest of positive results improved. Patients whose biologic mechanism persisted in being slug- gish, however, were then stimulated, or whipped, into conformity by a hypo- dermic intradermal injection of neomycin. Furthermore, the dermatologic lit- erature cautions the .observer not to be impatient in his search for positive skin tests. He is advised that delayed reactions are common. If early read- ings are negative, look again the reward will appear in 5 or 7 days. Since it takes about 5-7 days to "incubate" an allergic state where none existed be- fore, one should not really be surprised by the efficiency of this skin patch test technic, which is, unfortunately, the established procedure for demon- st-rating neomycin allergy. A startling piece of research in 1967 by Raab (2,3) revealed that neomycin shared a particularly basic chemical characteristic with a few other sub- stances, e.g., polymyxin B and compound 48/80. Raab showed that neomycin is capable of degranulating mast cells which pr. ovoke the release of histamine. Raab recognized that neomycin must have an allergy-producing potential similar to many other substances however, it is neomycin's mast cell depleting properties that are exceptional and have gone unrecognized. Skin testing with high concentrations or by intradermal injections of neomycin may elicit neo- mycin's particular irritant qualities, qualities that are not being separated from an allergic response (4).

156 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS A recent study by Schorr et al. (5) emphasizes reproducibility of test re- sults and convincingly separates neomycin reactors from nonreactors. How- ever, regretably, it d.oes not establish the nature of the process or processes that are responsible for the dermal reactivity. Within the patient population, neomycin dermatoses, as well as the skin tests for establishing them, may be the result of histamine release due to a chemical irritation rather than an allergic phenomenon. A noteworthy report which helps to purge neomycin of its onus considers the vehicle in which neomycin is presented to skin, suggesting that pene- trability through the epidermis is an important factor. Hjorth (6) in his 1968 review of neomycin reactors at the Finsen Institute emphasized: "In propor- tion to their sale creams, lotions and powders containing neomycin were rare- ly connected with sensitization. This investigation suggests that neomycin ointments are the major cause of sensitization to this antibiotic." How thorough is the neomycin overkill? Four years after publication of Raab's and Hjorth's reports a regulatory agency proposed to deny further certification of selected neomycin consumer products based on a literature review that did not include the work of either. Example IV A few years ago a dermatologist was shocked by the remark that the diag- nosis of hair-dye dermatitis in his patient due to an allergy to p-phenylene- diamine (PPD) was circumstantial at best and could scientifically be false furthermore, his admonition that the patient never dye her hair again may be needlessly condemning her for life to a hair color she finds most obnox- i,ous. The ease he presented was straightforward enough: a woman of 38 years was unhappy with her prematurely greying brown-black hair. It made her look and feel 10 years older. She was convinced it was creating domestic problems. For 2 years, .on a regular 8-10 week schedule, she had dyed her hair to its normal uniform color with great success and personal satisfaction. Twenty-four hours prior to each application a carefully executed skin patch test as described by the manufaeturer had been performed and found to be negative. However, the morning after the last hair coloring procedure, which was carried .out in every detail as to technic and product, exactly as those which preceded it, the patient awoke with redness, itching, roughness, and swelling about the ears and hair line with accentuation over forehead and upper eyelids. When the patient presented herself and her story to the same dermatolo- gist several hours later, the eruption had grown more severe. A tentative diagnosis ,of hair-dye dermatitis was made immediate treatment with topieal and oral eortieosteroids was instituted. Recovery was prompt and complete. A month later, as scheduled, the patient returned for a diagnostic 48-hour