photosensitivity

Photosensitivity is an umbrella term for abnormal skin or eye reactions triggered by light, most commonly ultraviolet radiation from the sun or artificial sources. Reactions may occur in otherwise normal tissues or indicate an underlying condition, such as a metabolic disorder, autoimmune disease, or exposure to a photosensitizing drug.

Reactions are classified as phototoxic or photoallergic. Phototoxic reactions resemble a sunburn and occur when a photosensitizing agent absorbs light and damages skin without immune involvement. Photoallergic reactions are immune-mediated and occur after sensitization, typically with certain topical agents or medications.

Endogenous photodermatoses include porphyrias and systemic lupus erythematosus, where inherent compounds or immune dysregulation cause light sensitivity. Exogenous forms arise from drugs or chemicals (for example tetracyclines, fluoroquinolones, sulfonamides, thiazide diuretics, amiodarone), or from contact allergens, such as fragrances or sunscreens.

Clinical features vary by type. Phototoxic reactions present as sunburn-like redness, swelling, and sometimes vesicles after exposure. Photoallergic reactions cause itching and eczematous rashes that may spread beyond sun-exposed areas. Photosensitivity can involve the eyes, with photophobia. Diagnosis relies on history, physical examination, and, when needed, phototesting and laboratory studies (porphyrin panels, autoimmune serology, or patch testing).

Management centers on sun protection and avoidance of triggers. Practical measures include broad-spectrum sunscreen with UVA/UVB coverage, protective clothing, hats, and sunglasses. Treat skin lesions with standard dermatologic care; address the underlying condition or adjust offending medications as appropriate. The prognosis varies by cause, but many reactions are preventable with careful sun exposure management.