What Does Skin Do? Skin, our largest organ, has many jobs. It: protects the network of muscles, bones, nerves, blood vessels, and everything else inside our bodies forms a barrier that prevents harmful substances and germs from entering the body protects body tissues against injury helps control body temperature through sweating when we're hot and by helping keep heat in the body when we're cold Without the nerve cells in skin, people couldn't feel warmth, cold, or other sensations. Every square inch of skin contains thousands of cells and hundreds of sweat glands, oil glands, nerve endings, and blood vessels. What Are the Parts of Skin? Skin has three layers: the epidermis (ep-ih-DUR-mis), dermis (DUR-mis), and the subcutaneous (sub-kyoo-TAY-nee-us) tissue. The epidermis is the upper layer of skin. This tough, protective outer layer is thin in some areas and thick in others. The epidermis has layers of cells that constantly flake off and are renewed. In these layers are three special types of cells: Melanocytes (meh-LAH-nuh-sites) make melanin, the pigment that gives skin its color. All people have roughly the same number of melanocytes; the more melanin made, the darker the skin. Exposure to sunlight increases the production of melanin, which is why people get suntanned or freckled. Keratinocytes (ker-uh-TIH-no-sites) make keratin, a type of protein that's a basic component of hair, skin, and nails. Keratin in the skin's outer layer helps create a protective barrier. Langerhans (LAHNG-ur-hanz) cells help protect the body against infection. Because the cells in the epidermis are completely replaced about every 28 days, cuts and scrapes heal quickly. Below the epidermis is the dermis. This is where our blood vessels, nerve endings, sweat glands, and hair follicles are. The dermis nourishes the epidermis. Two types of fibers in the dermis — collagen and elastin — help skin stretch and stay firm. The dermis also contains a person's sebaceous (sih-BAY-shiss) glands. These glands make the oil sebum (SEE-bum), which softens the skin and makes it waterproof. The bottom layer of skin is the subcutaneous (sub-kyuh-TAY-nee-iss) tissue. It's made of connective tissue , blood vessels, and cells that store fat. This layer helps protect the body from blows and other injuries and helps hold in body heat. What Does Hair Do? The hair on our heads doesn't just look nice. It keeps us warm by preserving heat. Hair in the nose, ears, and around the eyes protects these sensitive areas from dust and other small particles. Eyebrows and eyelashes protect eyes by decreasing the amount of light and particles that go into them. The fine hair that covers the body provides warmth and protects the skin. What Are the Parts of Hair? Human hair consists of: the hair shaft, the part that sticks out from the skin's surface the root, a soft thickened bulb at the base of the hair the follicle (FAHL-ih-kul), a sac-like pit in the skin from which the hair grows At the bottom of the follicle is the papilla (puh-PILL-uh), where the actual hair growth happens. The papilla contains an artery that nourishes the root of the hair. As cells multiply and make keratin to harden the structure, they're pushed up the follicle and through the skin's surface as a shaft of hair. Each hair has three layers: the medulla (meh-DULL-uh) at the center, which is soft the cortex, which surrounds the medulla and is the main part of the hair the cuticle (KYOO-tuh-kull), the hard outer layer that protects the shaft Hair grows by forming new cells at the base of the root. These cells multiply to form a rod of tissue in the skin. The rods of cells move upward through the skin as new cells form beneath them. As they move up, they're cut off from their supply of nourishment and start to form a hard protein called keratin. This process is called keratinization (ker-uh-tuh-nuh-ZAY-shun). As this happens, the hair cells die. The dead cells and keratin form the shaft of the hair. Hair grows all over the human body except the palms of the hands, soles of the feet, and lips. Hair grows faster in summer than winter, and slower at night than during the day. What Do Nails Do? Nails protect the sensitive tips of fingers and toes. We don't need our nails to survive, but they do support the tips of our fingers and toes, protect them from injury, and help us pick up small objects. Without them, we'd have a hard time scratching an itch or untying a knot. Nails can be an indicator of a person's general health, and illness often affects their growth. What Are the Parts of Nails? Nails grow out of deep folds in the skin of the fingers and toes. As epidermal cells below the nail root move up to the surface of the skin, they increase in number. Those closest to the nail root get flat and pressed tightly together. Each cell becomes a thin plate; these plates pile into layers to form the nail. As with hair, nails form by keratinization. When the nail cells accumulate, the nail pushes forward. The skin below the nail is the matrix. The larger part of the nail, the nail plate, looks pink because of the network of tiny blood vessels in the underlying dermis. The whitish crescent-shaped area at the base of the nail is the lunula (LOON-yuh-luh). Fingernails grow faster than toenails. Like hair, nails grow faster in summer than in winter. A nail that's torn off will regrow if the matrix isn't severely injured. Back to Articles Related Articles Ringworm Ringworm isn't a worm at all - it's the name for a type of fungal skin infection. The good news is that ringworm is easy to treat. Read More Jock Itch Jock itch is a pretty common fungal infection of the groin and upper thighs. It is generally easy to treat - and avoid - by following a few simple steps. Read More Dandruff If you're worried about dandruff, you're not alone. Dandruff can start in puberty, and lots of teens and adults live with it. Learn how to control it. Read More Melanoma Melanoma is different from other skin cancers because it can spread if it's not caught early. Find out how to lower your risk of getting melanoma and how doctors treat it. Read More Athlete's Foot Anyone can get athlete's foot. Find out how to avoid this itchy skin condition in this article for kids. Read More Your Skin No matter how you think of it, your skin is very important. It covers and protects everything inside your body. Read More Skin, Hair, and Nails Our skin protects the network of tissues, muscles, bones, nerves, blood vessels, and everything else inside our bodies. 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Learn more about this uncomfortable condition and what you can to do stop itching! Read More Athlete's Foot Although the name athlete's foot sounds funny, if you have this skin infection, you're probably not laughing. The good news is that it is generally easy to treat. Read More Impetigo Impetigo is a skin infection caused by fairly common bacteria. Read this article to learn how to recognize it and what to do about it. Read More Paronychia Paronychia is an infection of the skin around a fingernail or toenail. Most of the time, it's not serious. Find out what causes it, what to do, and how to prevent it. Read More Ingrown Toenails A toenail is ingrown when it begins to break through and grow into the soft skin of the toe. Find out more about ingrown toenails. Read More Dandruff Got flakes? Most cases of dandruff don't require a visit to a doctor's office. Treat them at home with special, over-the-counter dandruff shampoos. Read More Hives (Urticaria) Has your child broken out in welts? It could be a case of the hives. Learn how to soothe itchy bumps and help your child feel better. Read More Ringworm Ringworm is a type of fungal skin infection. The good news is that ringworm is easy to treat. Read More Athlete's Foot Athlete's foot is a common fungal skin infection. It's generally easy to treat and prevent. Read More Jock Itch Jock itch is a pretty common fungal infection of the groin and upper thighs. It is generally easy to treat and prevent. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.