Photoallergic contact dermatitis
Photoallergic contact dermatitis is an eczematous delayed type hypersensitivity response of the skin when affected by a combination of allergen and ultraviolet light (mostly UVA). Only previously sensitised persons can develop a photoallergic reaction. Common photoallergic agents include sunscreens, fragrances, antibacterial agents such as chlorhexidine, and drugs such as chlorpromazine and promethazine.
Clinical picture: Erythema, infiltration, blistering and, rarely, bullae occur in sun-exposed areas.
Distribution: Sun-exposed areas of the body are affected.
Diagnosis: Patient history regarding exposure to potential photosensitisers and a careful examination of the clinical features (distribution of the lesions, sparing of sun-protected areas) are mandatory. Cutaneous irradiation phototesting and photopatch testing may confirm the diagnosis.
Differential diagnoses: Phototoxic contact dermatitis, allergic contact dermatitis including airborne contact dermatitis, other photodermatoses such as polymorphic light eruption, chronic actinic dermatitis and erythropoetic protoporphyria must be taken into account.