Can the immersion time of PUVA bath therapy be shortened?

Up to now, there are only a few data available concerning the influence of bathing time on skin phototoxicity. We compared the erythemal responses of normal skin to bath PUVA with 8-methoxypsoralen (8-MOP) after 5, 10 and 20 min immersion time. Currently, 20 min is the routinely performed immersion time in many European countries, including Germany, while in other countries bathing times are shorter. The minimal phototoxic dose (MPD) following immersion times of 5 min and 10 min in a warm water bath (37 degrees C) containing 1 mg/l 8-MOP was compared to the MPD following 20 min immersion time in a half-sided manner in a total of 24 patients. Our results revealed that an immersion time of 5 min did not yield a detectable erythema after 72 h. In contrast, both 10 and 20 min PUVA baths induced visible erythemas with a significantly higher median MPD following 10 min immersion (2.25 J/cm2) compared to 20 min baths (1.5 J/cm2). As an erythemal response of 8-MOP PUVA bath seems reduced after shorter immersion times, comparative studies on the clinical efficacy using shorter time regimens have to be conducted before conclusive recommendations for clinical PUVA-bathing time can be given.