Correlation between bathing time and photosensitivity in 8-methoxypsoralen(8-MOP) bath PUVA

Bath PUVA (psoralen plus ultraviolet A) using 8-methoxypsoralen has become increasingly popular in recent years as an effective treatment option for a continuously expanding range of skin disorders. Among the various variable s of bath PUVA treatment, the impact of bathing time on photosensitivity ha s never been investigated in detail. We therefore determined the threshold UVA dose for erythema induction after different bathing periods. A marked i nfluence of bathing time on photosensitivity was found. Increasing the soak ing period from 5 min to 30 min resulted in a greater than 60% reduction of the minimal phototoxic and minimal perceptible phototoxic dose. Our result s demonstrate that the duration of the psoralen bath is a critical paramete r in bath PUVA treatment and has a major influence on UVA dose requirements .