How effective is narrowband UVB phototherapy for sun allergy?

Sun allergy, also called polymorphic light eruption, causes an itchy rash after exposure to sunlight in people whose skin reacts abnormally to light. Under supervision, small planned UVB exposures can help the skin tolerate light before a season or trip when flares are expected. The aim is prevention or reduction of symptoms, not permission to stay in strong sunlight without protection. The rash can vary in appearance, and a clinician may need to exclude medication-related photosensitivity or another light-triggered condition.

Discuss timing with a dermatologist because conditioning is planned before expected exposure rather than started during a severe flare. Attend sessions as directed and report redness that lasts, blistering, or worsening itch. Use shade, protective clothing, and broad-spectrum sunscreen as advised, and reapply it during outdoor activities. Check new medicines for photosensitivity warnings with a clinician or pharmacist. Keep a simple record of when the rash appears, where it occurs, and what type of light exposure preceded it.

Seek prompt advice if the eruption is severe, spreading beyond sun-exposed areas, or accompanied by facial swelling, breathing difficulty, fever, or marked illness. Contact the phototherapy clinic after a burn-like reaction. A rash that appears after minimal light, persists unusually long, scars, or involves the eyes or mouth needs medical review because it may not be typical polymorphic light eruption.

Ask whether your rash fits polymorphic light eruption, when conditioning should begin, which protection measures you need, and how to distinguish a treatment reaction from a flare.