Skin Bumps Caused by the Sun

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. The 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 seborheic keratoses, which are warty looking lesions that appear to be "stuck on" the skin. In contrast to actinic keratoses, seborrheic keratoses do not become cancerous.

Skin Cancer Caused by the Sun

The ability of the sun to cause skin cancer is a well-known fact. The 3 main skin cancers are melanoma, basal cell carcinoma, and squamous cell carcinoma. Melanoma is the most deadly skin cancer because it metastasizes more readily than the other skin cancers. It is believed that the amount of exposure of the skin to the sun before the age of 20 is actually the determining risk factor for melanoma. Basal cell carcinoma is the most common skin cancer and tends to spread locally, not metastasize. squamous cell carcinoma is the second most common skin cancer, and it can metastasize although not as commonly as melanoma. The risk of getting basal cell carcinoma or squamous cell carcinoma is determined by a person's lifetime exposure to UV radiation and the person's pigment protection.

http://dermatology.about.com/cs/skinanatomy/l/blsuneffect2.htm