Synergistic effect of broad-spectrum sunscreens and antihistamines in the control of idiopathic solar urticaria

BACKGROUND: It can be difficult to provide patients with idiopathic solar urticaria adequate protection from sunlight. In a nonrandomized controlled trial, we used a standardized phototest procedure to determine the effects of using sunscreen and antihistamine to control idiopathic solar urticaria. OBSERVATIONS: Three patients with idiopathic solar urticaria underwent phototesting with UV-B and UV-A radiation. The minimal urticarial dose (MUD) was determined 15 minutes after irradiation. The patients were subsequently tested with 5 times the MUD, and the reaction was graded every minute for 15 minutes. The patients were then treated with a high-protection, broad-spectrum sunscreen and a nonsedative antihistamine alone and in combination and underwent similar phototesting. The use of sunscreen allowed the patients to tolerate much higher doses of UV radiation (32-38 times the MUD on untreated skin). Antihistamine use did not increase the patients' MUD but did suppress wheal formation and itch, and only immediate erythema sharply located in the irradiated areas occurred. The combination of sunscreen and antihistamine acted synergistically and increased the tolerance to UV radiation markedly (80-267 times the MUD on untreated skin). Conclusion High-protection, broad-spectrum sunscreens and antihistamines protect patients with solar urticaria in different ways and are highly effective when combined.