A shield made of cells
The epidermis (ep-ih-DER-mis) is the top layer of your skin. It's the part you see when you look at your hand.
On most of your body it's very thin, about as thin as a sheet of paper. But it's tough. It's made of many rows of cells packed tight, like bricks in a wall.
The top layer has no blood vessels. It gets its food from the layer below. That's why a very light scratch may turn white but not bleed at all.
New cells at the bottom, old cells on top
At the very bottom of the top layer, cells are busy splitting in two to make new cells.
The new cells get pushed up slowly as more new cells form under them. On the way up, they fill with a tough protein called keratin (KER-uh-tin) and flatten out.
When they reach the top, they are dead, flat and hard, like tiny roof shingles. These dead cells are the part that keeps germs and water from getting through.
The trip from the bottom to the top takes about a month.
Little flakes everywhere
Every minute, your skin lets go of about 30,000 to 40,000 dead cells. They are so small you can't see them fall.
The flakes end up in your bed, your clothes and the air. House dust has some skin flakes in it, mixed with lots of other things, like dirt from outside, bits of fabric, pollen and pet hair.
Losing all those flakes is a good thing. It's how your skin stays fresh and new.
Color makers and thick spots
The bottom of the top layer is also home to melanocytes (muh-LAN-uh-sites). These cells make melanin (MEL-uh-nin), the coloring that gives skin its shade.
Special guard cells live in the top layer too. They spot germs and call your body's germ fighters for help.
The top layer is thickest on the palms of your hands and the soles of your feet. Those spots get pressed and rubbed the most, so they need extra armor.
If you walk barefoot a lot or swing on the monkey bars, those spots can get even thicker. A thick, tough patch like that is called a callus (KAL-us).