Clinical report demonstrates the necessity of sun-reactive skin typing for oral photochemotherapy dosing, highlighting limitations of relying solely on hair and eye color phenotype.
The concept of sun-reactive "skin typing" was created in 1975¹for a specific need: to be able to classify personswith white skinin order to select the correct initial doses of ultraviolet A (UVA) (in joules per cubic centimeter) in the application of the then newly developed technique for the treatment of psoriasis—oral methoxsalen photochemotherapy (PUVA).²The need arose as a result of experience with several patients who were a "dark" phenotype (brown or even black hair, and some with brown eyes) but, to our surprise, developed severe phototoxic reactions following oral ingestion of 0.6 mg/kg of methoxsalen and then, two hours later, were exposed to 4 to 6 J/cm². These initial doses were obviously too high, and it was then understood that the estimation of the white-skinned person's tolerance level to oral PUVA could not be based solely on the phenotype (hair and eye color).
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Thomas B. Fitzpatrick (1988) studied this question.
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