Skin is the largest organ of the human body with a surface area of 1.5-2.0 square meters in an average adult. Skin is 2-3 mm thick, and each 5 square cm of skin may have up to 600 sweat glands, 20 blood vessels, 60,000 melanocytes and over a thousand nerve endings.

The outermost layer of the skin is called epidermis (from Greek "epi" meaning "over"). Among many functions of the skin are protection, sensation, heat regulation, excretion of sweat and water resistance (to keep essential nutrients from washing out of the body).

5 square cm of human skin may contain up to 50 million bacteria, and on oily surfaces the amount of bacteria may reach 400 million per 5 sq. cm. However, these bacteria are so small they all could fit on one pea.

Though oily skin is especially prone to pore clogging and blackheads (caused by increased activity of oil glands), such skin is less prone to wrinkling and other signs of aging as oil keeps the moisture locked into the surface layer of the skin.

The thicker the skin, the more layers of cells with melanin (color pigment) in them it has, and therefore the darker its color.

Mammalian skin usually has hairs (or fur) that mainly serve as additional insulation.

Animal skin can be used to make such products as gelatin and glue.

Dogs, cats, rodents and primates all lick their wounded skin instinctively because saliva contains enzymes and other substances that contribute to wound healing.