Skin cancer is an abnormal growth of skin cells. It generally develops in areas that are exposed to the sun, but it can also form in places that don’t normally get sun exposure.The two main categories of skin cancers are defined by the cells involved. The first category is basal and squamous cell skin cancers. These are the most common forms of skin cancer. They’re most likely to develop on areas of your body that get the most sun, like your head and neck. The second category of skin cancers is melanoma. This type of cancer develops from cells that give your skin color. These cells are known as melanocytes. Benign moles formed by melanocytes can become cancerous.