fotodermatitis

Fotodermatitis is an inflammatory skin condition triggered by exposure to light, typically ultraviolet A (UVA) or ultraviolet B (UVB), in combination with a chemical, drug, or underlying disease. The term covers several mechanisms and includes phototoxic reactions, photoallergic reactions, and other light-associated dermatoses such as those seen in porphyrias.

Phototoxic reactions are non-immunologic and dose-dependent. They occur when a photosensitizing agent absorbs light and directly damages skin cells, producing a sunburn-like eruption after sufficient exposure. Photoallergic reactions are immune-mediated, require prior sensitization, and manifest as an itchy, eczematous eruption that may spread beyond sun-exposed areas.

Common triggers include medications such as tetracyclines, fluoroquinolones, sulfonamides, nonsteroidal anti-inflammatory drugs, amiodarone, and retinoids; plant-derived furocoumarins (psoralens) in citrus oils and other preparations; coal tar, fragrances, and certain other topical agents. Metabolic conditions such as porphyrias can cause light sensitivity independent of external agents.

Clinically, fotodermatitis presents with erythema, edema, vesicles or bullae, and pruritus in sun-exposed regions, often progressing to burning sensations. Diagnosis relies on history of exposure to light and a triggering substance, supported by specialized testing such as photopatch testing or phototesting when a photosensitizing agent is suspected.

Management emphasizes avoidance of triggers and rigorous photoprotection, including broad-spectrum sunscreen (UVA/UVB) and protective clothing. Offending drugs are discontinued when possible. Inflammation is treated with topical corticosteroids and antihistamines for itch; severe cases may require systemic therapy. Prognosis improves with removal of triggers, though some individuals experience persistent sensitivity or pigmentary changes.