What is skin cancer?

Skin cancer starts in the cells of the top layer of skin (called the epidermis). A cancerous (malignant) growth is a group of cancer cells that can grow into nearby tissue and destroy it. The cancerous growth can also spread (metastasize) to other parts of the body, but this is rare with most skin cancers.

The skin is the body's largest organ. It covers your entire body and protects you against harmful factors from the environment such as the sun, hot temperatures and germs. The skin controls body temperature, removes waste products from the body through sweat and is where you feel touch. It also helps make vitamin D.

The 3 most common skin cancers are basal cell carcinoma, squamous cell carcinoma and melanoma.

Basal cell carcinoma starts from the basal cells, which are the cells found in the deepest part of the epidermis.

Squamous cell carcinoma starts from the squamous cells, which are the cells found above the basal cell layer.

Melanoma starts from the melanocytes, which are the cells found in the deepest part of the epidermis along with the basal cells. Melanocytes often group together to form non-cancerous moles on the skin.

Basal cell carcinoma and squamous cell carcinoma are often grouped together and classified as non-melanoma skin cancer because they develop from skin cells other than the melanocytes. They also act differently than melanoma. Non-melanoma skin cancers tend to grow slowly, and they are often found early. Melanoma can spread into nearby tissue and to other areas of the body. Non-melanoma skin cancers are also treated differently than melanoma.

Find out more about non-melanoma skin cancer and melanoma.

Rare types of skin cancer can also develop. These include Merkel cell carcinoma, Kaposi sarcoma and skin lymphoma.

Melanoma can also develop in the eye. Find out more about eye cancer.