phototoxic

Phototoxic refers to a type of adverse cutaneous reaction that occurs when a chemical substance on the skin or in the body is activated by light, typically ultraviolet A (UVA), resulting in tissue damage that resembles an exaggerated sunburn. Unlike photoallergic reactions, phototoxic reactions are not immune-mediated and can occur in anyone given sufficient dose of the agent and light exposure. The reaction is dose-dependent and does not require prior sensitization.

Mechanism involves a photosensitizing compound absorbing photons and reaching an excited state, often transferring energy to oxygen to form reactive oxygen species. These reactive species cause cellular damage to lipids, proteins, and DNA, leading to erythema, edema, pain, and sometimes blisters. The process is influenced by the amount of photosensitizer present, the intensity and duration of light exposure, and the individual’s skin type.

Common causative agents include tetracycline and other antibiotics, fluoroquinolones, sulfonamides, amiodarone, nonsteroidal anti-inflammatory drugs, coal tar, psoralens in certain plants, and some essential oils or cosmetics. The reaction typically occurs on sun-exposed areas and can occur after the first exposure if a sufficient amount of agent and light are present. Risk is higher for individuals with fair skin or high cumulative sun exposure.

Diagnosis and management rely on history of chemical exposure and recent sun exposure. Discontinuation or avoidance of the offending agent, sun protection (clothing, broad-spectrum sunscreen), and limiting UV exposure are important. Mild cases may be treated with cool compresses and topical corticosteroids for inflammation; analgesics can help with pain. Severe or persistent reactions require medical evaluation.

See also: photoallergy, photodermatitis, photosensitivity.