fototoxikusak

Fototoxikusak are substances that become toxic to biological tissue upon exposure to light, typically ultraviolet or visible wavelengths. They include drugs, chemicals, dyes, and certain plant-derived compounds. When individuals or samples containing these substances are illuminated, the energy absorbed can trigger chemical reactions that damage cells and tissues, especially in sun-exposed skin or eyes.

The underlying mechanism often involves absorption of photons by the substance, entering an excited state, and transferring energy to molecular oxygen to form reactive oxygen species. This leads to lipid peroxidation, protein modification, and DNA damage. Phototoxic reactions are dose-dependent and non-immune in origin, with the severity correlating with the chemical concentration and the duration and intensity of light exposure. Onset is usually within minutes to hours after exposure and typically resembles a sunburn in exposed areas.

By contrast, photoallergic reactions are immune-mediated and require prior sensitization; they may spread beyond the immediately illuminated skin and are not purely dose-dependent.

Examples and contexts: many antibiotics (for instance doxycycline and other tetracyclines; fluoroquinolones) can be phototoxic, as can certain nonsteroidal anti-inflammatory drugs such as ketoprofen and naproxen, and the antiarrhythmic drug amiodarone. Psoralens and related furocoumarins used in PUVA therapy are deliberately phototoxic. Plant-derived compounds (furocoumarins in some citrus fruits, celery, parsley) can cause phytophotodermatitis when combined with sunlight or UV exposure. Coal tar and some dyes also have phototoxic potential.

Prevention and safety: assess phototoxic risk in pharmaceuticals, cosmetics, and occupational chemicals; use shielding, protective clothing, and appropriate sunscreens; discontinue or substitute offending agents if reactions occur. See also phototoxicity and photosensitivity.