Melanoma is a cancer that most often starts in the skin. The skin is the body’s largest organ. It protects your body from injury, infection, heat and ultraviolet light from the sun. The skin helps control your body temperature and gets rid of waste materials through the sweat glands. It also makes vitamin D and stores water and fat.
The skin has 2 main layers. The top layer at the surface is called the epidermis. Below the epidermis is the inner layer, called the dermis. The dermis contains nerves, blood vessels, sweat glands, oil (sebaceous) glands and hair follicles. The epidermis is made up of 3 types of cells:
- Squamous cells are thin flat cells on the surface of the skin.
- Basal cells are round cells that lie under the squamous cells. They are continually made deep in the epidermis. Newly made basal cells push the older cells toward the surface of the skin, where they become squamous cells.
- Melanocytes are also found deep in the epidermis, in between the basal cells. Melanocytes make melanin, which gives colour to your skin. When skin is exposed to the sun, the melanocytes make more melanin and cause the skin to tan or darken. Sometimes melanocytes cluster together and form moles (also called nevi). Moles are common and are usually not cancerous.
Different types of cancer can start in the different types of skin cells.
- Squamous cell skin cancer starts in the squamous cells.
- Basal cell skin cancer starts in the basal cells.
- Melanoma starts in the melanocytes.
Melanoma is less common than squamous cell and basal cell skin cancers (sometimes called non-melanoma skin cancers). Melanoma can start in other places in the body where melanocytes are found, such as the eyes, mouth and vagina or under the fingernails. These types of melanoma are rare.