What is Epidermis? - Definition, Function & Layers

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  • 0:01 What is the Epidermis?
  • 0:35 Function
  • 1:30 Layers
  • 3:38 Cells
  • 4:51 Lesson Summary
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Lesson Transcript
Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

In this lesson, learn what the epidermis is as well as how it functions. Discover more about it as well as explore the actual cells it is comprised of.

What is the Epidermis?

When we think of protecting our bodies from the elements, we may think of putting on a jacket, or shoes and socks. Perhaps you use sunscreen, and wear a hat and sunglasses. Fortunately, in addition to what we wear, we also have a built-in protective covering that keeps our insides safe from our external environment. Our skin, the largest organ in our body, serves this crucial purpose with a layer known as the epidermis as our first line of defense. In this lesson, we will take a closer look at this skin layer and gain an understanding of why it is so important to our body.

Function of the Epidermis

The epidermis is the outermost layer of our skin. Tough and resilient, protection is its number one job. Think of a parka you may wear in the winter. The inside is lined with soft fleece, providing a layer of warmth. But the outside is made of a strong waterproof material that lets nothing through. It is a similar situation with our own epidermis.

Cross-Section of Skin
Cross section of skin

The protective qualities of our outer layer are vast. Our epidermis is waterproof, which is why we don't swell with liquid each time we bathe. The cellular structure of the epidermis also forms a highly effective barrier against germs. When skin is healthy and intact, it is difficult for bacteria and viruses to make an entrance. In addition, cells of the epidermis have the miraculous ability to regenerate, or grow back, unlike many other cells in the body. When we suffer from a wound, healthy skin heals and replaces damaged cells with ease.

Layers of the Epidermis

The epidermis is composed of four main strata, or layers. The outermost layer is called the stratum corneum, which is Latin for ''horny layer.'' While we aren't literally covered in horny scales, this layer is tough nonetheless. It also varies in thickness depending on the body part it covers. If you often go barefoot, the stratum corneum on the sole of your foot is probably quite thick. Compare that to the skin on your eyelids and you can see the drastic difference.

Layers of the Epidermis

If we were to take a closer look, we find that the stratum corneum is composed almost exclusively of dead cells. It may come as no surprise that we lose skin cells on a regular basis. In fact, the dead cells of the stratum corneum slough off so often that we end up with a completely new outer layer about every 35 days.

And how, you may be wondering, do we have any skin left if we are always losing cells? This is where the stratum basale comes in. Just as its name suggests, it is the base or deepest layer of the epidermis. A cell-producing factory, the basale layer contains stem cells which are constantly dividing to make new ones. These fresh new cells make their way up to the stratum corneum to replace those that have sloughed off. This cycle runs on a continual basis, keeping our epidermis healthy and strong.

Cross-Section of Epidermis under Microscope
Cross-Section of Epidermis

Two additional layers are sandwiched between the stratum corneum and stratum basale. The stratum spinosum borders the stratum basale. Here we find spiny keratinocytes that help bond other cells together. Finally, the stratum granulosum lies beneath the stratum corneum. Cells in this layer produce a waxy material that aids in waterproofing the skin.

While most of our body's epidermis is made up of four layers, on the palms of our hands and the soles of our feet, there is one extra layer of skin. The stratum lucidum is a translucent layer that provides extra thickness to these areas of the skin.

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Additional Activities

Crossword Puzzle on the Definition, Functions, and Layers of an Epidermis


This activity is linked to the lesson on the role of the epidermis in the skin. For this activity, complete the crossword by filling in a word that fits each of the given clues. You can right-click the crossword to save the image and print it. With a pencil and an eraser, neatly write your answers in the boxes provided.


3. This protein is a key structural material found in the stratum corneum.

6. A waterproof layer of the skin which serves as the first line of protection against germs.

9. A tough layer of the epidermis that sheds about every 35 days.

10. The largest organ in the body which consist of stratified epithelial cells.


1. Damaged cells in the epidermis are easily _____ with new ones.

2. Cells that help regulate the immune system.

4. Keratinocytes reside in this layer of the skin, sandwiched between the stratum corneum and stratum basale.

5. The foundation of the epidermis that contains constantly dividing stem cells.

7. A natural pigment that protects the skin from intense ultraviolet radiation.

8. It is a thin, translucent layer that lowers the friction in the palm and soles in the feet.

Answer Key

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