Skin cancer occurs when the body does not repair damage to the DNA inside skin cells, allowing the cells to divide and grow uncontrollably. Skin cell damage may be caused by a variety of factors, including genetics and skin type. But most cases of skin cancer are caused by overexposure to ultraviolet (UV) light produced by the sun. Skin cancer may appear as a dark spot, lesion, a wound that does not heal or a bump on the skin. The type of skin cancer depends on the cells that are damaged. For example:
- Basal cell carcinoma, the most common type of skin cancer, is caused by damage to basal cells that sit just below the skin’s surface.
- Squamous cell carcinoma is cancer of the cells on the surface of the skin. Squamous cells also make up the lining of the digestive and respiratory systems and the inner lining of hollow organs, such as the kidneys.
- Melanoma may occur when melanocytes are damaged. These cells give skin its pigment and darken the skin when it is exposed to the sun.
- Merkel cell carcinoma develops in the cells that give skin its ability to sense touch. That’s why these cells, which are nestled below the skin, next to nerve cells, are sometimes called touch cells.
- Kaposi's sarcoma (KS): This type of skin cancer may appear as purplish blotches or lesions on the skin (usually on the face or legs), but it may also form inside the mouth or in lymph nodes. In rare cases, lesions may develop in the lungs, causing breathing problems.
- Lymphoma of the skin: Lymphoma, which is cancer of the lymphatic system, may form in a variety of locations in the body, including the spleen, lymph nodes, thymus and skin. This cancer may appear as red or purple patches, moles or pimples on the skin that may itch or ulcerate. Other symptoms may include fatigue and weight loss.
Skin cancer incidence
Skin cancer is the most common form of cancer in the United States. Each year, more than 3 million cases of skin cancer are diagnosed. Most skin cancers are non-melanoma, and if caught early, may be treated by a dermatologist in an outpatient procedure. Melanoma comprises only about 2 percent of all skin cancers, but it is responsible for more than 90 percent of skin cancer deaths.