Photoallergic dermatitis from 8-methoxypsoralen.

A 36 year old woman with psoriasis vulgaris developed generalized photoallergic dermatitis to 8-methoxypsoralen after 16 uneventful treatments with 8-methoxypsoralen und UVA (PUVA). The diagnosis of photoallergy was confirmed by re-exposure to oral 8-methoxypsoralen and total body UVA irradiation; phototests using topical and oral 8-methoxypsoralen with a high intensity monochromator or with a new high intensity light apparatus for the delivery of UVA; and histological studies. Photoallergy occurred only with UVA, but not with UVB or UVC. There was no photoallergy following trimethylpsoralen.