Photoallergic contact dermatitis

Abstract

Topical photoallergic contact dermatitis (PACD) is thought to represent a delayed-type hypersensitivity reaction when an exogenous agent combines with some component of the skin in the presence of ultraviolet (UV) and/or visible light. Although PACD is relatively rare, it is also underdiagnosed as a cause of sunlight-exposed site dermatitis. Photopatch testing is the investigation of choice for topical PACD and a European consensus methodology for photopatch testing should allow greater comparison between centers. Currently, organic UV sunscreen filters and topical nonsteroidal anti-inflammatory drugs (NSAIDs) are the commonest photohaptens encountered by patients. Clinicians should be aware of potential new photohaptens in the environment and have a low threshold for photopatch testing such agents.