The skin is the largest organ of the body. It covers the body, protecting it from injury, regulating its temperature and controlling fluid loss. Skin, like all other body tissues, is made up of cells. Its two main layers are the epidermis and dermis.
This is the outer layer of the skin. It contains three types of cells:
- squamous cells – flat cells that are packed tightly to make up the top layer
- basal cells – tall cells that make up the lower layer
- melanocytes – cells that produce a dark pigment called melanin, the substance that gives skin its colour.
Basal cells multiply constantly and the older cells move upwards in the epidermis. When they flatten out and form a layer they become squamous cells. The top layer of your skin is made up of dead skin cells which eventually fall off. The three main types of skin cancer begin in the cells of the epidermis.
When skin is exposed to the sun, melanocytes make extra melanin to protect the skin from getting burnt. This is what causes skin to tan. Melanocytes are also in non-cancerous (benign) spots on the skin called moles or naevi. Most moles are brown, tan or pink in colour and round in shape.
This is the layer underneath the epidermis. It contains the roots of hairs, sweat glands, blood and lymph vessels, and nerves. Before a skin cancer can spread, it must first move into the dermis.