What Is Skin And How Does It Work?

Oh skin…such an incredible organ. To do what it does every day from the day we’re born until our final breath. Ensuring our protection from outer evils.

Wow. Poetic much?

Skin is pretty amazing, I will say. But what exactly is skin? We all know it’s the largest organ and we know it protects us from germs and other environmental factors. For this post, I will explain what skin is made of, how it works, and what it does.

What Is Skin?

To understand what skin is, we need to know how skin is divided first.

Skin is made up of three different layers: the epidermis, the dermis, and the hypodermis (or subcutaneous layer). These three layers have differing functions from one another, but they all work in tandem to create what we know and see as skin.

The epidermis is the top, outermost layer of the skin. It’s composed mainly of keratinocytes (skin cells). The epidermis is further divided into five layers, starting at the top: the stratum corneum (horny layer*), the stratum lucidum (thin layer), the stratum granulosum (granular layer), the stratum spinosum (spiny layer), and the stratum germinativum or stratum basale (basal cell layer). *Get your mind out of the gutter.

“Dang. That’s a lot of layers.”

Yes, that is a lot of layers. Keep in mind we’re talking about cells though, so they’re microscopic. And these layers are made up of these microscopic things. And these microscopic things have jobs. To keep it simple, they all have specific functions they perform to make skin look the way it does and perform its protective duties.

The top layer, the stratum corneum, is basically the first layer of protection. The skin cells it’s composed of have hardened into protective cells called corneocytes. There’s about 15-20 layers of these cells forming the stratum corneum, although I’ve heard other professionals say a higher or lower number. I’m assuming it varies from person to person, but this is what I was taught and what I’ve learned.

The layer below that, the stratum lucidum, is pretty thin. And also sometimes up for debate. There’s not much to say about this layer.

The next layer, the stratum granulosum, is composed of cells filled with keratin (the protein skin cells are made of). This is the layer where keratinization (the process where keratin is bound to cells) and barrier formation happens. Skin cells are held together by a lipid barrier, otherwise they’d just fall right off us all the time. And that sounds too scary.

The layer under that, the stratum spinosum, is where stuff is going on. I’m talking cell division, enzymes creating lipids and proteins, stuff is active. This is where the party is taking place.

The last layer of the epidermis, the stratum basale, is located just above the dermis. It’s composed of a single layer of basal cells (a type of stem cell) which undergo continuous mitosis (that thing cells do to divide themselves) to replenish the regular loss of skin cells being shed from the top layer. This layer also contains melanocytes, pigment producing cells that are in charge of, well… producing pigment.

Pretty straightforward so far, right? Top layer of skin is made up of 5 other layers that make skin look like it does. Cool beans!

The layer below the epidermis is the dermis**. This layer plays a support role, being primarily comprised of connective tissues made of collagen proteins and elastin fibers. It supplies the skin with oxygen and nutrients, and it’s also, you guessed it, divided into more layers! Yay, layers!

Luckily, it’s only two layers, as far as I’m aware. The dermis is divided into the papillary layer, which basically connects the epidermis and the dermis together, and the reticular layer, which is the denser and deeper layer of the dermis. The reticular layer is made up of mainly collagen and elastin, and when damage is done to these elastin fibers, we start to see sagging, wrinkles, and overall aging.

The dermis is also called corium, cutis, or even “true skin”. I can see why the would call it that, but I feel it undermines skin and how skin works in general. That’s like saying pinky toes aren’t true toes. Or, wait… no, it’s like saying big toes are “true toes”. Yeah… that’s’ what I meant. It doesn’t make sense.

The last and deepest layer is the hypodermis**. In the most simplest terms, and because this post is getting very long, it’s a layer of mostly adipose tissue (fat cells) that creates a protective cushion. This layer thins and decreases with age.

Okay, I know I promised a lot at the beginning of this post, but it’s getting late and this post is getting very long. I don’t want to overwhelm anyone (especially me) so I will stop here for today. I will continue with this topic next week!

**These layers are beyond my expertise. I may have outdated or wrong information when it comes to the dermal layer and the hypodermic layer. If you have any questions, comments, or concerns about any of the information provided above, feel free to let me know!