Have you ever noticed strange, exaggerated sun burn-like skin conditions or skin lesions (any abnormal change on the skin) after being out in the sun? Such symptoms may be caused by photosensitizing (sun sensitizing) chemicals in your medication or cosmetics that produce a biological reaction when exposed to ultraviolet (UV) light. This UV light may come from the sun, tanning bed or other types of artificial UV light like "purple-lighted" mosquito zappers and would normally not give a person problems. Photosensitizing agents can cause two basic types of reactions - photoallergies or phototoxicity.