The skin is the largest organ of the body. It serves many important functions, including protecting the body from infection, and regulating body temperature and fluids.

The skin is primarily composed of three layers. The epidermis is the outer layer of skin and contains basal and squamous cells. Melanocytes are also found in the epidermis. These are cells that contain pigment, which allows the skin to tan and which also protect the deeper layers of skin from the effects of UV sunlight exposure.

The dermis, which lies below the epidermis, contains blood vessels, connective tissue, hair follicles, and sweat glands. The subcutaneous layer, which is the deepest layer of skin, contains fat cells and collagen.

Skin cancer occurs when there is an uncontrollable growth of abnormal cells in a layer of the skin. There are three common forms of skin cancer that are distinguished by the types of cells affected.

Basal cell carcinoma is the most common form of skin cancer. This type of skin cancer does not typically spread, but does require treatment. Basal cell carcinomas most often develop in areas of the skin exposed to the sun.

Squamous cell carcinomas develop in the middle layer of the epidermis. This type of cancer can spread and can be life threatening if not treated appropriately.

Abnormal growths of melanocytes, called malignant melanomas, are the most aggressive form of skin cancer. Melanomas can spread quickly to other parts of the body and to organs. This type of skin cancer can be fatal if not detected and treated early. People with fair skin are at increased risk for developing this form of cancer.

Increased sun exposure and a history of sunburns increase the risk for developing skin cancer.