Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types: basal cell cancer, squamous cell cancer and melanoma. The first two together along with a number of less common skin cancers are known as nonmelanoma skin cancer. Basal cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin, that may be shiny with small blood vessel running over it or may present as a raised area with an ulcer. Squamous cell cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds. Greater than 90% of cases are caused by exposure to ultraviolet radiation from the sun. This exposure increases the risk of all three main types of skin cancer. Exposure has increased partly due to a thinner ozone layer.