Skin Cell Factory T e bottom of the epidermis is a skin cell factory. New, live cells are constantly made there. T e new cells push up on the ones above them. In this way, live cells slowly get pushed to the top of the epidermis. Aſt er two or three weeks, the cells reach the surface and die. T ey become part of your protective shield. It may seem strange to shed skin cells so


oſt en. Yet some animals take shedding to a diff erent level. A snake sheds its entire outer skin all at once. You don’t because your skin stretches as you grow. A snake’s skin doesn’t. So snakeskin can’t grow as the snake grows. Instead, about every six weeks, the snake molts. Its outer skin dies and then splits open. T e snake slithers out, sporting a brand new, larger skin. T e old, grayish outer skin is leſt behind. Animals like frogs and salamanders molt,


too. T eir skin splits in the back. T en the animal uses its forearms to pull off its skin. Unlike a snake, the frog or salamander eats its old skin.


This catfi sh’s skin helps it fi nd food and avoid danger.


Keep in Touch You know some of the jobs the epidermis does. Now here’s something that it doesn’t do. If you cut or scrape it, your epidermis won’t hurt or bleed. It can’t. T ere aren’t any nerves or blood vessels in the epidermis. T e next layer of skin, however, is packed with them. For example, imagine running your hand


over the soſt bristles of a paintbrush. Now think about touching the stiff bristles of a toothbrush. T ink about wrapping your hand around a frosty glass of lemonade. Now picture holding a steaming mug of hot chocolate. Even if your eyes were closed, you could


tell one object from another. You would know whether something feels smooth, rough, cold, or hot because of your sense of touch. You can thank the nerves in your dermis for this sense.


Sending Signals T e dermis is the second layer of skin. It’s loaded with nerves. In fact, the dermis has about 72 km (45 miles) of them. Nerve endings sense changes in the environment. T e nerves send electric signals to your brain. T en you feel the sensations. All this happens faster than you can blink. Humans have a lot of nerves in their dermis.


You might think that humans have the best sense of touch of any creature. T e truth is we’re not even close. Many animals have a more developed sense


of touch than we do. T e catfi sh is a good example. It doesn’t have scales. It has smooth skin. T is increases its sensitivity to touch. T e catfi sh’s sensitive mouth and whiskers help it fi nd food in dark or muddy waters. Tiny hairs along the sides of its body pick


up on movement in the water. It can sense a fi shing line moving in the water and swim away from it.


Fast Fact: You grow a new set of outer skin cells every month.


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