Topical application of sulisobenzone (Uval) is shown to prevent the long-wave ultraviolet light-induced phototoxic reaction in skin treated topically with psoralen. This suggests that unintentional or unwanted exposure to solar long-wave ultraviolet radiation can be avoided, making topical psoralen treatment of vitiligo safe and manageable.
Parrish JA, Pathak MA, Fitzpatrick TB. Prevention of Unintentional Overexposure in Topical Psoralen Treatment of Vitiligo. Arch Dermatol. 1971;104(3):281-283. doi:10.1001/archderm.1971.04000210055009