Skin, outer body covering of an animal. The term skin is commonly used to describe the body covering of any animal but technically refers only to the body covering of vertebrates (animals that have a backbone). The skin has the same basic structure in all vertebrates, including fish, reptiles, birds, and humans and other mammals. This article focuses primarily on human skin.
The skin is essential to a person’s survival. It forms a barrier that helps prevent harmful microorganisms and chemicals from entering the body, and it also prevents the loss of life-sustaining body fluids. It protects the vital structures inside the body from injury and from the potentially damaging ultraviolet rays of the sun. The skin also helps regulate body temperature, excretes some waste products, and is an important sensory organ. It contains various types of specialized nerve cells responsible for the sense of touch.
The skin is the body’s largest organ—that of an average adult male weighs 4.5 to 5 kg (10 to 11 lb) and measures about 2 sq m (22 sqft) in area. It covers the surface of the body at a thickness of just 1.4 to 4.0 mm (0.06 to 0.16 in). The skin is thickest on areas of the body that regularly rub against objects, such as the palms of the hands and the soles of the feet. Both delicate and resilient, the skin constantly renews itself and has a remarkable ability to repair itself after injury.
II. STRUCTURE OF THE SKIN
The skin consists of an outer, protective layer (epidermis) and an inner, living layer (dermis). The top layer of the epidermis is composed of dead cells containing keratin, the horny protein that also makes up hair and nails.
The skin is made up of two layers, the epidermis and the dermis. The epidermis, the upper or outer layer of the skin, is a tough, waterproof, protective layer. The dermis, or inner layer, is thicker than the epidermis and gives the skin its strength and elasticity. The two layers of the skin are anchored to one