Time course of PUVA erythema.

Optimization of the PUVA regime requires knowledge of the time-course and dose-response characteristics of PUVA erythema. Although existing guidelines recommend determination of the minimal phototoxic dose (MPD) 72 hours after UVA exposure and treatment administered 72 hours apart, recent evidence suggests that maximal PUVA erythema occurs beyond this time point, and hence the current assessment time underestimates the phototoxic effect of PUVA. This report reviews the current literature, including the authors' own experience of the characteristics of PUVA erythema, and recommends that the optimal time to read the PUVA MPD is 96 h.