The skin

Aooow-ouch! Beep-blip-beep-ping! No! I am not about to die... OUCH!

AAAH-OUCH!... Don't you think this tattoo is making me look cooler? Beep-blip-beep-ping! Human skin is soft, and sensitive, full of nerve endings. Nerves make it possible to feel things like touch, even really light touch. ...

and small changes in temperature. Brr, stop that! Skin is amazingly good at sensing the world around you. And there's a lot of skin: about two square meters, on an adult human. Skin works like a giant sensor, that perceives signals from its surroundings.

Skin is very strong, and flexible. It keeps fluids inside, so the body doesn't dry out... ... but it can also release fluid, as sweat, when the body needs to be cooled down. Skin contains fat, that works as insulation, and helps us keep warm. Skin also makes an effective protection against bacteria, viruses, and dirt.

Most substances and organisms simply can't penetrate the skin. Human skin is also a little factory. Using energy from the sun, the skin produces vitamin D, that the body needs. If you look closely, you'll see that skin is made up of three layers. Deepest in, is a layer called the hypodermis, or subcutis.

There you'll find plenty of fat. It helps us keep warm, and it protects the inside of the body against impact. Throughout the hypodermis there are also cavities, where water can be stored. Just like the fat, this water functions as an extra supply for the body. On top of the hypodermis is the dermis.

It consists of connective tissue, that makes it strong and flexible. The dermis is full of blood vessels that can expand, and contract. In this way, they regulate how much blood is circulating through the skin. When the body needs to cool down, the vessels widen so much that the warm blood travels all the way to the skin to cool down. When it's cold, the vessels instead contract, so that the warm blood is kept deeper inside the body.

The dermis also contains nerves. They end either as a bunch of free nerve endings or encapsulated in connective tissue. Free nerve endings react to pain. Encapsulated nerve endings react to various things: pressure, heat, cold, or touch. The dermis also contains hair follicles, and glands that release sweat and a kind of fat: sebum.

This fat helps to make the skin soft and smooth. Above that is the epidermis, which is the thinnest layer of the skin. The outermost cells there are old and dead, and harder than young cells. That's the corneum. The corneum prevents substances from penetrating the skin, and protects the skin from wear and tear.

This layer can get even thicker when it gets rubbed a lot. That's why you get calluses on your hands when you work hard. Just imagine that; two square meters of soft and flexible tissue, that can receive signals, change temperature, produce vitamins. And gets thicker when you rub on it. What a super material!

Blipp blopp blluuuuu-up? What's that? Can the skin deal with anything? Nah, not really. Watch out for the sun.

A bit of sunlight is good for you, but too much damages the skin. It can lead to skin cancer. Clothing and sunscreen give protection.. and shade, of course. Strong chemicals, like paint and solvents, can actually penetrate the skin.

That's why we use protective clothing. If you use makeup and don't wash it off before you go to bed, you can get rashes. But the skin is better off if it isn't washed too often. It can get dry from too much soap and water. Aah?

Looks pretty neat, uh? Hellooo? Ta daaa! Ouah-hah-haaah.