What is "phototoxicity"

n. Any adverse effect due to exposure to light, especially such effects on the skin

Phototoxicity, also called photoirritation, is a chemically induced skin irritation, requiring light, that does not involve the immune system. It is a type of photosensitivity.

The skin response resembles an exaggerated sunburn. The involved chemical may enter into the skin by topical administration or it may reach the skin via systemic circulation following ingestion or parenteral administration. The chemical needs to be "photoactive", which means that when it absorbs light, the absorbed energy produces molecular changes that cause toxicity. Many synthetic compounds, including drug substances like tetracyclines or fluoroquinolones, are known to cause these effects. Surface contact with some such chemicals causes photodermatitis; many plants cause phytophotodermatitis. Light-induced toxicity is a common phenomenon in humans; however, it also occurs in other animals.