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  • Writer's pictureThalia Polk

Skin. Part 2

In my original post, Skin., I provided a brief introduction to our skin and the three layers that it contains. In this new post, I dive into the epidermis, explaining its five layers, desquamation, and barrier function. It all begins in the bottom, innermost layer...

5. The Stratum Basale

The stratum basale, also known as the stratum germinativum, is the layer where the skin cells germinate, making this layer one of the most important layers in the skin. Since it is the deepest epidermal layer, it is the layer that is closest to the blood supply lying underneath the epidermis.

Stratum basale is a single layer of thick, column-shaped cells called basal cells. The basal cells divide via mitosis, creating keratinocytes. Keratinocytes comprise 95% of the cells in the epidermis. The cells in the stratum basale bond to the dermis via the basement membrane (this is a topic for a future post!).

Every day, millions of new cells arise in the stratum basale. Over time, the new cells force the older cells to migrate into the upper layers of the epidermis through a process called DESQUAMATION, or, cellular turnover. As the cells migrate to the top layer, their shape, nucleus, and chemical composition change - beginning in the stratum basale as brand new keratinocytes and ending up as dead cells on the surface of our skin that flake off into thin air. The desquamation process takes between 25 and 45 days, depending on age, sun exposure, diet, water intake, and other factors.

4. Stratum Spinosum

Here, the cells change from their column-like shape to more of a polygon shape that appears spiny when viewed through a microscope, giving this layer its name, stratum spinosum. The spiny protrusions hold the cells tightly together, preventing the skin from tearing and blistering. Thus, the stratum spinosum is partly responsible for the skin's strength and flexibility.

It is in this layer that the cells begin to make keratin. Keratin is a tough, fibrous protein that makes up the main structure of the skin.

3. Stratum Granulosum

The stratum granulosum is a thin layer that is responsible for the production of the two layers above it - the stratum lucidum and the stratum corneum. The cells in this layer are flattening, becoming more brittle, and will lose their nuclei. Meanwhile, their membranes are thickening.

The cells generate large amounts of keratin and keratohyalin proteins through a process called keratinization, and accumulate as lamellar granules within the cells, making up the bulk of the keratinocyte mass, giving this layer its grainy appearance.

2. Stratum Lucidum

The stratum lucidum is also known as the clear layer because of its translucent appearance under a microscope. This layer is only found in the palms of the hands, the fingertips, and the soles of the feet. It consists of two to five layers of flattened, dead keratinocytes. The thickness of the stratum lucidum is controlled by the rate of division of the epidermal cells.

1. Stratum Corneum

The Stratum Corneum is the outer-most layer of the epidermis - the layer we can see and feel. It is also known as the skin barrier.

The keratinocytes have now become very flat, are tightly packed, and cornified. No longer referred to as keratinocytes, they are now called corneocytes. They have no nucleus and almost no water. They are more of a protein mass than a cell, as they are dead skin cells filled with tough keratin protein. Corneocytes are surrounded by lipids that help repel water.

The stratum corneum helps limit TEWL (Trans-Epidermal Water Loss) and acts as a barrier providing protection from environmental toxins and harmful microorganisms such as bacteria, fungi, and insects. It also stores important enzymes, hormones, and cytokines, as well as provides antioxidant and immune support.

What happens when the barrier function is compromised?

When the stratum corneum experiences damage it signals the production of Langerhans cells. These cells detect threats and trigger immune cells to respond, which in turn creates inflammation.

How can you protect the barrier function of your skin?

  • Wear sunscreen

  • Use skincare products that are appropriate for your skin type and condition.

  • Keep hydrated - inside and out

  • Take it easy on the exfoliators

  • Use moisturizer

  • Get professional facials regularly

Do you need assistance getting your skin in shape? Visit my website to view my entire menu of services, email me at, or DM me via Instagram or Facebook! I'll get you set up with a comprehensive consultation and skin analysis, and we'll sail off on your skin transformation journey together!



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