pho·to·toxic \¦fōd.ōˌ\adjective Etymology:phot- + toxic 1.: rendering the skin susceptible to damage (as sunburn or blisters) upon exposure to light and especially ultraviolet light < phototoxic antibiotics > < a phototoxic topical agent > 2.: induced by a phototoxic substance < a phototoxic response > • pho·to·toxicity\"ˌ \noun