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Hand Eczema Phototherapy — SCE Dermatology MCQ

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HardPhotobiologyHand Eczema PhototherapySCE Dermatology

A patient develops eczema on sunscreen-treated sites only after sunlight exposure. Which test distinguishes photoallergic contact dermatitis from ordinary allergic contact dermatitis?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: C — Paired photopatch testing with one allergen set irradiated by UVA

Photopatch testing applies duplicate allergen series and exposes one set to a measured UVA dose. A stronger reaction confined to the irradiated site supports photoallergy, whereas equal reactions to both sets support ordinary contact allergy.

Reference: https://academic.oup.com/bjd/pages/bad-guidelines