UV radiation causes an increased number of moles in sun-exposed areas. Sun exposure also causes precancerous lesions called actinic keratoses that develop especially on the face, ears, and backs of the hands. They are small crusty bumps that can often be felt better than they can be seen. Actinic keratoses are felt to be premalignant lesions because 1 in 100 cases per year will develop into squamous cell carcinoma. UV exposure also causes seborrheic keratoses, which are warty looking lesions that appear to be "stuck on" the skin.