9O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS attention is focused on the substitution of a hydrogen for a methyl group at the R• position. This alters one of the central rings at the meso position and suggests a possible analogy with compounds which have an anthracene-like structure and whose photosensitizing capacity can be increased by change of one or more of the meso or para atoms of the central ring (22). The precise molecular specificity is shown by the effect that structural alteration has on the erythemal activity of furocoumarins and makes the difference between an inert and active compound (5). Thirdly, light of an effective (proper) wavelength, and in adequate quantity, must reach the skin. Hence source, exposure time, atmos- pheric conditions, thickness of stratum corneum, and melanin content all may cause differences in quantity of light reaching the epidermal cell. The specific band of light which elicits the photosensitivity reaction is the action spectrum. Each photosensitizer has its own specific absorption spectrum, which usually matches the action spectrum but not always. The only radiant energy capable of producing photodynamic action is the ultraviolet or visible. Some examples are: Fluorescent dyes (3900- 7900 A) sulfonamides, chlorpromazine, demethylchlortetracycline (2900-3100 A) 8 methoxypsoralen (2700-3200 A). Finally, oxygen is necessary (2, ,5). Diagnosis is complicated because one has to decide whether a partic- ular reaction is photoxic or photoallergic. As Baer and Harber point out, the morphological characteristics of the eruption and a knowledge of the incidence of the adverse reaction and the concentration of the drug necessary to evoke it are often crucially important in arriving at a decision. Also, tests used in making a diagnosis of drug-induced photo- sensitivity are usually based on reproducing the lesions under controlled conditions with known types and amounts of artificial light (23). Treatment for acute phases of photodermatitis is similar to that used in treating other dermatoses (24) usually rapid improvement occurs if the photosensitizing agent and sunlight in the responsible wavelength spectrum are avoided. (Received November 18, 1965) REFERENCES (1) Epstein, S., J. Invest. Dermatol., 2, 43 (1939). (2) Blum, H. F., Photodynamic Action and Diseases Caused by Light, Reinhold, New York, 1941. (3) Lamb, J. H., et al., Arch. Dermatol. and Syptz., 62, 1 (1950).

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