Skin cancer develops when DNA in skin cells becomes damaged so that the body cannot repair them, and these damaged cells begin to grow and divide uncontrollably. As the damaged cells multiply, they form a tumor. Since skin cancer generally develops in the epidermis, the outermost layers of skin, a tumor is usually clearly visible. This makes most skin cancers detectable in the early stages.
Skin cancer is most often caused by ultraviolet (UV) radiation from the sun. UV light is invisible and causes sunburn and sun tan. This radiation damages the DNA which leads to the development of cancerous skin cells. Some cases of skin cancer may be hereditary and some children may inherit abnormal genes from parents. Anyone with a family history of skin cancer also has an increased risk of developing skin cancer.
Skin cancer develops in people of all skin colors, from the palest to the darkest. However, skin cancer is most likely to occur in those who have fair skin, light-colored eyes, blonde or red hair, a tendency to burn or freckle when exposed to the sun, and a history of sun exposure. In dark-skinned individuals, melanoma most often develops on non-sun-exposed areas, such as the foot, underneath nails, and on the mucous membranes of the mouth, nasal passages, or genitals. Those with fair skin also can have melanoma develop in these areas.