Lesson 1
Your body's raincoat
Your skin is your body's biggest organ. It wraps around your whole body to keep water in and germs out.
Skin is made of layers, like a stack of pancakes:
- The epidermis (ep-ih-DUR-mis) is the outer layer, the part you can see and touch. It's made of skin cells stacked on top of each other.
- The layer underneath holds blood tubes that bring food and oxygen, sweat makers that cool you down, the roots of your hairs, and nerve cells that feel touch.
Wow!
A grown-up's skin, spread out flat, would be about 2 square meters, about the size of a big blanket!
Lesson 2
A brand new outside, all the time
At the bottom of the epidermis, skin cells divide to make new cells. The new cells push the older ones up toward the top.
As the cells move up, they get flat and dry and fill up with a tough stuff (the same kind of stuff your hair and nails are made of). By the time they reach the top, they're no longer alive. They make a tough, waterproof outer layer, and then they flake off.
- A skin cell's trip from the bottom to the top takes about a month.
- You lose tens of thousands of tiny skin flakes every minute. They're too small to see!
Try this
Scroll up to the 3D model and press Watch skin grow to see cells rise and flake off.
Lesson 3
Skin color and sunshine
Some special cells in your skin make melanin (MEL-uh-nin), a brown color. They share it with the skin cells around them.
Inside each skin cell, the melanin sits on top of the nucleus like a tiny umbrella. It helps shade the cell's DNA from the sun's strong rays.
- Everyone has about the same number of melanin-making cells. Different skin colors come from how much melanin they make.
- Freckles are little spots with extra melanin.
- Even with melanin, too much sun can burn your skin. Sunscreen, hats, and shade help protect it!
Lesson 4
Healing cuts and feeling the world
When you get a cut, your skin gets right to work:
- 1. Blood makes a sticky plug that dries into a scab, like a bandage your body makes itself.
- 2. White blood cells rush in to fight any germs.
- 3. Skin cells at the edges divide and crawl across under the scab to close the gap.
- 4. When the new skin is ready, the scab falls off. (Don't pick it!)
Your skin also helps you feel. Tiny nerve endings sense touch, heat, cold, and pain, and send messages to your brain.
Try this: the two-point test
Close your eyes. Have a friend gently touch your fingertip with either one or two pencil tips close together. Can you tell how many? Now try it on your arm. Fingertips have lots more touch sensors, so they're much better at it!
Quiz
Skin cell quiz