Skin is the largest organ on the human body. It creates a protective layer against heat, light, the environment, injury and infection. It helps regulate the body's temperature, converts vitamin D to its active form, stores water and fat, prevents entry of bacteria and other germs into the body and acts as a vital sensory organ. On average, an adult has between 18 and 20 square feet of skin and this skin weighs about six pounds.

There are three major layers to skin:

Epidermis. This is the outer most layer that sloughs off dead skin cells and acts as a protective barrier against foreign bodies, infections and the sun. The epidermis also contains the cells (melanocytes), which are responsible for skin pigmentation. In addition, this layer plays a role in immune system processes.

Dermis. The middle layer of skin, the dermis houses hair follicles, sebaceous (oil) glands, sweat glands, nerves, capillaries (small blood vessels) and lymph vessels. Collagen, elastic and other substances make this layer tough enough to protect the body and withstand both simple and serious insults. The numerous sweat glands are a vital part of the body's temperature regulatory system. The dermis also contains touch, vibration, temperature and pain receptors.

Subcutaneous Tissue. This is the deepest layer of skin and it contains larger blood vessels and nerves. It is made up of a network of connective tissue and fat cells and plays an important role in the metabolism, protection against injury and temperature regulation.