Getting above it all: Hey, your epidermis is showing!

Your epidermis is really strong. The majority of the cells that make up the epidermis are called keratinocytes. Keratinocytes are filled with an exceptionally tough, fibrous, protein known as keratin. Just as your skin has more then one layer (epidermis, dermis, and subcutaneous layer), the epidermis itself has three layers. Within these layers, there’s constant cellular motion going on.

Outer layer
The outermost layer of the epidermis is known as the stratum corneum, also known as the horny layer. This layer provides your body with a durable overcoat that protects deeper cells from damage, infection, and from drying out.

This layer of your skin is actually made up of dead skin cells. (Your hair and nails are made of dead cells too!) So when you look at your skin, you’re really seeing skin that is dead. But these deceased skin cells only stick around for a little while.

Soon, they flake off — like when you wash, scratch yourself, go shopping, sit in class, fall asleep, and even read this book. Basically, all the time. In fact, every minute of the day we lose about 30,000 to 40,000 dead skin cells off the surface of our body.

Middle layer
This layer is known as the stratum spinosum. The cells in this layer looked kind of spiny to the scientists who first described them.

Inner layer
Known as the basal layer, the inner layer is like a production facility for the new skin cells (keratinocytes) that eventually make their way up through the stratum spinosum to the outer stratum corneum to replace the dead older cells you lose from the surface.

The keratinocytes in the basal layer stand up like little soldiers at attention on what’s called the basement membrane, a barrier that separates the epidermis from the dermis; it’s the anchor that joins the epidermis and dermis together.

The keratinocytes are kept alive by the underlying dermis — which serves as their blood supply because the epidermis has no blood supply of its own. But their upward journey carries them farther away from their supply lines, and as they approach the top, they begin to die.

By the time they’ve reached the outer layer of the epidermis, they’ve lost virtually all of their cellular contents except for tough keratin fibers and other solid proteins. Even as they dry up and die, they become much more resilient and durable and become the flattened cells that form the stratum corneum.

This one-way trip takes about two weeks to a month to accomplish. Figure 2-2 demonstrates the process. When an injury or an acne pimple penetrates the basement membrane, a scar may result. (I describe acne scarring in Chapter 16.)