SKIN, HAIR, AND NAILS
The visible part of your skin, hair, and nails is mostly dead. The surface is the final resting place for cells that once grew below. The skin is the body's largest organ. It acts as a barrier against wetness, sun damage, and infection. The sweat and oil glands of the skin, exocrine glands, offer two types of protection. Perspiration cools the skin as it reaches the surface, and the oil glands prevent skin and hair from dryness and keep bacteria out. The hard surface of the nail protects the sensitive tips of the fingers and toes. Hair traps air next to the body, which reduces heat loss, and helps keep us warm. The hair, skin, nails, and exocrine glands are all part of a protective network called the integumentary system.