7. Birthmarks and moles
Birthmarks, moles and warts are normal and most of the time they are harmless or benign. However, if you develop a mole or wart in an area that is recently exposed to the sun, it may a symptom of melanoma. Also, if a birthmark or mole suddenly changes colour can be another indication of cancer. Senile and actinic keratosis are triggered by the sun and UV rays can be considered precancerous skin changes.