To understand skin cancer, it helps to know a few basic facts about normal skin - the crucial organ that separates the inside of your body from the outside world.
People often don't think of the skin as being a body organ, but that's what it is. In fact, it is the largest organ in your body. It has a surface area of about two square yards and weighs between six and nine pounds. This huge organ performs several different functions:
1. Your skin protects your body. It acts as a barrier to bacteria, viruses, and other contaminants, and it covers your internal organs, protecting them from the environment and cushioning them against injury. Certain cells in the skin, called melanocytes, also help to protect you against ultraviolet light from the sun. However, this natural protection is not enough to prevent sunburn or skin cancer, especially in light-skinned people, so it is important to take precautions to protect yourself from too much sun exposure.
2. Your skin is a sense organ. Its nerve endings give you the sense of touch, which allows you to recognize hot, cold, pain, pressure, and a variety of other sensations.
3. Your skin helps to regulate the internal temperature of your body. The production of sweat in glands in the skin helps to cool your body when it is exposed to excessive heat.
4. When you sweat, your skin excretes salt and other waste products from your body.
5. Your skin produces vitamin D in response to exposure to sunlight. Fortunately, though, this isn't the only way to get vitamin D. Vitamin D is also present in certain foods, especially vitamin D-fortified milk, and in vitamin supplements. So you can get plenty of vitamin D without being out in the sun at all.
The skin has three layers. You can see a picture of them HERE
From top to bottom, the three layers are the epidermis, dermis, and cutis.
The epidermis is only about 1/100 of an inch (0.2 mm) thick. It protects the deeper layers of the skin. Most of the cells in the epidermis are keratinocytes, which are also called squamous cells. Another type of cells, called basal cells, are found at the bottom of the epidermis, just above the dermis. You will see these cell names again in the pages on this site that discuss specific types of skin cancer affecting these cells. Melanocytes - cells that produce the brown pigment melanin - are also found in the epidermis. Melanin gives your skin its color and helps to protect the inner layers of skin against ultraviolet rays from the sun.
The dermis, or middle layer of the skin, is much thicker than the epidermis. It contains hair follicles, sweat glands, blood vessels, and nerves. The various types of cells in the dermis are held together by a protein called collagen, which is responsible for the skin's strength, elasticity, and resilience.
The deepest layer of the skin, the cutis, conserves heat and helps to protect the body from being injured.