Joan Cartan-Hansen, Host: Your skin is one of the most important organs in your body.

But look a little closer.

It isn't just one long sheet.

It's a complex collection of cells, nerves, blood vessels and glands.... [MUSIC] Student One: Boy, is it hot out here.

Student Two: Yeah, did you want some sunscreen?

Student One: Why would I want sunscreen?

Student Two: To protect your skin.

Student One: I don't need to protect my skin.

Cartan-Hansen: You better believe you do.

Your skin is like a coat of armor.

It shields your bones and protects your internal organs from being hurt.

It helps regulate your temperature.

It keeps out germs and helps you feel things.

Without skin, you wouldn't survive.

Student Two: Tell me more.

Cartan-Hansen: Well, the outside layer of skin is known as the epidermis.

It's remarkably elastic and in most places, covered with a fine coat of hair.

It is a tough layer that's waterproof and seals out invading germs.

But it wears away, shedding millions of dead skin cells every minute.

And underneath new cells constantly replace the old.

The layer beneath that is the dermis, which is packed with blood vessels, nerves, hair follicles and sweat glands.

A network of fibers, elastin and collagen, hold and connect this layer together.

Below that is the hypodermis.

This layer connects to the bones and muscles underneath.

It also contains fat cells that insulate the body and acts as a cushion to protect the body from blows.

The fat also serves as an energy reserve.

And, when you are overweight, that layer is where the extra fat is stored.

Student One: That's interesting.

But, I'm still hot.

Cartan-Hansen: Well, the skin does play a very important role in keeping you the right temperature.

When you get too hot, sweat oozes up and out tiny holes called sweat pores on to your skin.

Even your fingertip has dozens of sweat glands just below the surface.

Sweat cools your body by evaporation.

And when you are too cold, the blood vessels in your skin get narrower and tiny muscles pull the fine hair on your body upright to trap air and create a layer of insulation.

Your skin works to regulate your body's temperature to keep you feeling just right.

And feeling is something your body does too.

Touch is the first sense we develop.

Inside our skin, we have millions of tiny touch sensors that send signals to our brain, detecting everything from the prick of a pin point to our movement in the world around us.

But not all parts of our skin are equally sensitive.

Lips and hands have more touch sensors than our back or legs.

If every part of our body was drawn in proportion to how sensitive it is to touch...this is what your body would look like.

And what part of your body has the most touch sensors...why, the tip of your tongue.

Student Two: Really?

Cartan-Hansen: And your skin has an amazing ability to mend itself.

When you get a cut, your skin automatically starts to block infectious bacteria from getting in and to keep fluids from leaking out.

Blood clots and cells multiply from all sides until the wound is healed.

And as you age, your skin becomes less elastic and you get wrinkles.

By the way, the color of your skin depends on how much melanin it contains.

Below the first layers of skin are special pigment cells that make melanin.

When your skin is exposed to the sun, more melanin is pushed into the skin.

People whose ancestors lived in and around the equator have darker skin to protect themselves from the harsher sun.

Those who came from nearer the poles didn't get as much sun, so their skin didn't need as much melanin so it stayed lighter.

And freckles are just bits of melanin in the skin.

But melanin can't completely protect your skin.

If you get too much sun, you get a red sun burn.

Sun burns can actually damage your skin.

And that can lead to premature aging of the skin as an adult.

And excessive sun exposure is the leading cause of skin cancer.

So, every time you go out in the sun use sun screen.

Take care of your skin and your skin will take care of you.

Student One: Hand me the bottle.

Cartan-Hansen: If you want to learn more about the skin, check out the science trek website.

You'll find it at science trek dot org.

[MUSIC] ANNOUNCER: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges, by The Friends of Idaho Public Television and by the Corporation for Public Broadcasting.