Factors influencing methoxsalen phototoxicity in vitiliginous skin

• A series of experiments were conducted to determine the optimum conditions required to induce methoxsalen phototoxicity in vitiliginous skin. The results revealed that optimum phototoxicity could be obtained only when a lapse of at least 15 minutes was allowed between the application of the drug and exposure to long-wave ultraviolet light (UVA). The duration of methoxsalen's phototoxic potentiality, after its application to skin, varied in direct proportion to chemical concentration. Although a high chemical concentration and low dosage of UVA was a less time-consuming method of inducing phototoxicity, our results indicate that lower concentration and longer UVA exposure were less likely to induce undesirable blistering reactions. (Arch Dermatol112:327-332, 1976)