Skin

The thin layer of tissue forming the natural outer covering of the body of a person or animal.

Skin is your body's largest organ. If you could peel off and weigh the average adult's skin, it would weigh between 6 and 8 pounds and would cover about 20 square feet — about the size of a twin size blanket. Now, that's a lot of skin!

Your skin has many important jobs. This super organ is waterproof, helps keep germs out, helps regulate your temperature, protects your inner organs, and helps you “feel” things. In fact, you couldn't live without it!

Just like your heart or your lungs, your skin is a body organ that is part of an organ system. The integumentary system consists of everything that comes in contact with the outside world: the skin, hair, nails, and glands. In animals, the system may include feathers, scales, or hooves. The integumentary system is the body's first line of defense against the outside world. It works with all the other systems of the body to maintain the right conditions for your body to function.

Skin is made up of three layers: the epidermis, the dermis, and the subcutaneous layer, or hypodermis. The part of skin you see when you look at your body is called the epidermis, the outermost layer of skin. It is made up of several layers of cells. Cells in the epidermis produce a protein called keratin, which makes the skin waterproof and tough. The epidermis is thickest on the soles of your feet and the palms of your hands, but is much thinner on your elbows and around your eyes. Tiny holes called pores that allow sweat to escape are part of the epidermis.

The cells on the outside layer are constantly dying and flaking off. Your skin loses 30,000 — 40,000 cells every minute! Over the course of a year, you will lose between 5 and 10 pounds of dead skin flakes! But don't worry, there are plenty more where they came from. Deep in the epidermis, new cells are constantly being formed and pushing their way up to the top. New skin cells last for about a month before flaking off. Your epidermis continually renews itself throughout your life.

Your epidermis also has cells called melanocytes. These cells produce a pigment called melanin, which is what gives skin its color. Freckles are clumps of melanocytes that show up as spots on your skin. The amount of melanin you have helps determine the color of your skin. The more melanin you have, the darker your skin is. When you go out in the sun, your body makes more melanin to try and protect your skin from getting sunburned. Melanin is where your suntan comes from. But, melanin alone isn't enough protection for your skin. You need to help protect your skin by using sunscreen, covering up with clothing, or staying in the shade.

The second layer of your skin is called the dermis. This layer of skin contains the follicles where hairs grow. This layer also has sweat glands, oil glands, blood vessels, and nerve endings, all of which help keep your skin healthy. Blood vessels keep your skin cells healthy by bringing them the oxygen and nutrients they need, while oil glands keep your skin soft and smooth. There are also flexible fibers called collagen running through the dermis, which give your skin its strength and elasticity. As people get older, their bodies make less collagen and produce less oil. That's why older people usually have skin that is thinner and looser.

The third and bottom layer of the skin is called the subcutaneous layer, also known as the hypodermis. It is made mostly of fat cells and helps your body stay warm. It also provides you with a bit of cushioning to help protect your body from bumps and falls. The subcutaneous layer contains connective tissue that attaches your dermis to your muscles and bones, in order to bind your skin to all the tissues underneath it.

Zits, pimples, lumps, bumps — also known as acne. What is it, and why does it appear on so many teenagers' faces? Anyone can have pimples, but it happens to teenagers more often than adults and children. About 85% of teenagers have some form of acne. Acne happens when your body produces too much oil, also known as sebum. Sebum, produced in the sebaceous glands located in the dermis layer of your skin, helps keep your skin lubricated and protected. But too much of a good thing can turn into a problem. The “extra” oil, combined with bacteria and those dead skin cells your body is always shedding, can clog up your pores or hair follicles, which leads to a pimple. Experts say the best thing you can do for a pimple is to leave it alone. Learn more about acne.

Sometimes your skin might develop a rash, which may cover a little or a lot of your body. A rash is often red, itchy, or bumpy. A rash can happen for a variety of reasons. Usually a rash is your body's way of alerting you that something's not quite right. Some people get rashes if they eat a food they're allergic to, or come in contact with certain plants. Others may get a rash from a certain type of clothing, soap, medicine, chemical, or metal. Most rashes go away on their own, but it's important to let a parent or other adult know about it.

What are scars? Injuries to the skin, such as cuts, scratches, and scrapes, are quite common. When your skin is injured, there may be a break in the skin. If you are bleeding, it means you've torn through the epidermis and left the dermis exposed. Because your skin is no longer a barrier to outside germs, it's important to clean and bandage the cut immediately, so that it is protected while it heals. Skin is amazing in the way it repairs itself. The skin makes collagen fibers that act like bridges to reconnect the broken tissue. A temporary crust called a scab forms over the wound while the damaged skin heals underneath. Eventually, the scab dries up and falls off, sometimes leaving a scar if the damage was severe. A scar is repaired skin that doesn't have hair or sweat glands and may be a slightly different color from your regular skin.

Skin is like a huge sensor packed with nerves for keeping your brain in touch with the outside world. Your skin works with your nervous system to allow your sense of touch to function. Your dermis contains receptors, or nerve endings, that help you feel the things you touch. When your skin comes in contact with something, these nerve endings send signals to your brain telling it how that substance feels. Different kinds of receptors can receive different sensations, such as texture, temperature, pressure, pain, and friction. These nerve endings tell your brain when something is soft or prickly, smooth or rough.

The nerve endings in the dermis also help to keep you from getting hurt. If you touch something hot, the nerve endings send a message to your brain saying, “Hey, that's hot!” Your brain sends back a message for you to move your hand away quickly. Your skin is always working to keep you safe. Learn more at Science Trek's Nervous System page.

Your body works best at 98° Fahrenheit. Your skin helps keep your body at the right temperature by helping it cool down and protecting you when it is cold.

When you get overheated, your body needs to lose heat. Your skin helps you lose heat by expanding the blood vessels in the dermis to increase blood flow to the surface of the skin. That's why your face gets red when you exercise! It also helps by pouring on the sweat. On one square inch of your body, you have about 650 sweat glands! When you're hot, your body produces more sweat, which comes to the surface through your pores. Sweat helps take the heat away from the skin as it evaporates, helping your body cool down. Just think of it as your own personal air conditioning unit!

When your body is cold, your skin stops heat from escaping by constricting the blood vessels and using the muscles in the hair follicle to make the hair stand up straight to form goose bumps. The goose bumps help trap a layer of warm air next to your skin.

When it comes to being one amazing organ, the skin wins! It covers us up and protects our inner organs, lets us feel the world around us, prevents dehydration, and acts as a barrier to keep disease and bacteria out of our bodies. The skin provides cushioning to keep us from getting hurt and temperature control for our bodies. It's the one organ that lives on the outside of the body; it is the link between the outside world and all our other body systems. Your skin works hard for you every minute of the day!

Return the favor to your skin by taking good care of it. Keep your skin clean by washing often. Be careful around sharp objects, wear protective gear when you play sports, and stay safe in the sun. Stay in the shade, drink lots of water to replenish sweat, and always use sunscreen when you're outdoors. No matter what color skin you have, the sun's UV rays can burn you or do damage that you might not even see or feel until you're older.

• Human skin is home to millions of beneficial bacteria known as skin microbiota.
• Everyone is born with unique fingerprints. No two prints are exactly alike.
• Your skin also makes Vitamin D when the sun shines on it. Vitamin D is important for the health of your bones and other parts of your body
• Sweat is produced by the skin when you are hot, but it may also be produced when your nervous system is “overstimulated” – like when you are very anxious.
• Birds have feathers on their skin, reptiles have scales, and all mammals have some form of hair on their skin. These “extensions” from the skin are part of the integumentary system.
• A rhinoceros has skin that is extremely thick, up to 2 inches (5 cm) deep.
• When you look at a polar bear you see white fur, but their skin is actually black.
• Frogs don't drink water, but they absorb the water they need through their skin. They also absorb much of the air they need through their skin. Earthworms are also “skin-breathers” — they get all of their oxygen this way.
• People think that snakes have slimy skin, but snakeskin is actually dry and smooth.
• In the ocean, creatures such as barnacles often make their homes by attaching themselves to the skin of whales.
• Some vegetables and fruits, such as potatoes and apples, are referred to as having “skin!”