Other forms: photosensitized
To photosensitize is to make something more vulnerable to the effects of light. A side effect of some medications is to photosensitize the patient's skin, making sunblock extra important.
If something photosensitizes you, it makes you much more sensitive to the sun's ultraviolet rays. Sometimes skin cream or prescription treatments can photosensitize your skin, putting you at risk for sunburn. The equivalent reaction can happen to animals as well — eating buckwheat plants can photosensitize horses, for example. This word comes from the Greek root photo, "light," and the Latin sentire, "feel."