The skin is the largest organ of the body. It protects the body from infection and prevents the loss of too much water and other fluids. The skin sends messages to the brain about heat, cold, touch and pain sensations.

The skin has three layers: the epidermis, dermis and subcutis (fat).

The top layer of the skin is the epidermis. The epidermis is a thin layer of skin that protects the deeper layers of skin and the organs. The epidermis is composed of four layers. The lower layer is made up of basal cells. A layer called the basement membrane, just under the basal layer, separates the epidermis from the other layers of skin.

The dermis, the middle layer, is much thicker than the epidermis. It contains hair shafts, sweat glands, blood vessels and nerves.

The last and deepest layer of the skin is called the subcutis. The subcutis keeps in heat and has a shock-absorbing effect, which helps protect the body's organs from injury.

	Basal cell carcinoma is the most common type of nonmelanoma skin cancer.

Nonmelanoma skin cancers are by far the most common type of cancer worldwide. There are several types of nonmelanoma skin cancers. The two most common are basal cell carcinoma and squamous cell carcinoma. Both can usually be successfully treated.

Basal cell carcinoma begins in the lowest layer of the epidermis, the basal cell layer. Basal cell carcinoma accounts for about 75 percent of all skin cancers. It usually begins on the areas of the body most exposed to the sun, such as the face, neck, forearms and back of the hands.

How basal cell carcinoma looks

Squamous cell carcinoma begins in the upper layer of the epidermis and accounts for about 20 percent of all skin cancers. It also typically appears on the areas of the body most exposed to the sun, such as the face, ears, neck, lips and backs of the hands.

How squamous cell carcinoma looks