The 5 Layers of Your Skin
Your skin is the largest organ of your body. It is comprised of three main layers: the epidermis, dermis, and hypodermis. The epidermis is the topmost layer of skin – the one you can see and feel on the surface. It contains four to five layers (depending on body location), each with an important role.
These 5 layers constantly renew themselves in a process called Exfoliation and desquamation of the skin.
Image is used with permission from Baumann, L. S., & Baumann, L. (2009). Cosmetic dermatology. McGraw-Hill Professional Publishing.
1. Stratum Basale or Basal Layer
The deepest layer of the epidermis is called the stratum basale, sometimes called the stratum germinativum. This is where stem cells are located. Because this layer is the innermost layer, many topical products that you apply to the surface of your skin cannot reach this layer and have an effect. That is why applying stem cells to your skin’s surface is a waste of time – the uppermost layers of the skin prevent large compounds like stem cells from reaching this deep layer.
The basal layer is where new skin cells known as “keratinocytes” are “born.” As they are produced, these new cells travel upward, pushing existing older cells even higher in a process known as “keratinization”. Eventually, these skin cells reach the outer layer of your skin, where they push off dead, flaky cells and replace them. This process can take 26-40 days and is affected by age, genetics, hydration and cosmeceutical products.
Two other types of cells are also found here: Merkel cells and melanocytes. Merkel cells are receptors that send messages to your brain that get translated as your sense of touch. You have lots of these cells on the palms of your hands and the soles of your feet. Melanocytes produce melanin, which is the pigment that gives your skin and hair their color.
Overactive melanocytes produce too much melanin and can lead to uneven skin pigmentation.
2. Stratum Spinosum or the Spiny layer
This layer gives the epidermis its strength. Like its name suggests, the stratum spinosum contains spiny protrusions that hold the cells tightly together to prevent your skin from tearing and blistering.
3. Stratum Granulosum or the Granular Layer
This important layer has tiny granules full of components that are produced by skin cells and packaged in the granules. Keratin, which is what gives your strength, is packaged in little keratohyalin granules. Epidermal skin cells are named “keratinocytes” because they produce keratin. The keratinocytes in this layer also produce lipids and natural moisturizing factor (NMF) that make your skin waterproof and help it to hold onto moisture. The lipids, proteins, and natural moisturizing factors are produced in this layer inside “keratohyaline granules.” These granules are produced by the keratinocytes in the granular layer. It’s called the granular layer because of the presence of these granules.
In the upper layers of the epidermis (the stratum lucidum and stratum corneum), the granules break open to release their contents into the space between the cells. This bathes the stratum lucidum and the stratum corneum with important lipids that make up the skin barrier and many protective proteins. Overuse of hydroxy acids, retinoids, and other exfoliating ingredients can damage this important layer.
4. Stratum Lucidum
The stratum lucidum gets its name from the fact that the granules are no longer there, so the cells look clear or lucid. This thin layer of cells is found only in the thick skin on the palms of your hands and fingers and the soles of your feet.
5. Stratum Corneum
This is the outermost layer of the epidermis and is therefore exposed to the atmosphere outside of your body. There are usually 15 to 30 layers of cells in the stratum corneum, which play an important protective role. The cells in this layer help to prevent bacteria, viruses, and fungi from penetrating to deeper layers of skin, as well as provide protection against abrasion and friction for the more delicate underlying layers. This is the layer that makes the skin feel rough when it is dry.
The “skin barrier” that prevents evaporation of water is also located here. The entire stratum corneum layer is replaced with new cells in a process known as desquamation. New cells travel up from the basale layer where they are made and push out the old, lackluster cells on the surface. This process usually takes about four weeks. Cosmetic procedures like microdermabrasion smooth the surface of this layer, which makes skin reflect light and look more radiant.
Understanding skin science and how your skin works to protect and rejuvenate itself will help you properly care for it. If your skin is naturally very dry, for example, you can use skincare products that will help to strengthen your skin barrier to keep moisture in and harmful bacteria out. Oily skin types can use products that control excess lipids on the surface of their skin.
For more skincare science and recommendations from Dr. Leslie Baumann, be sure to follow @SkinTypeSolutions or @BaumannCosmetic on Facebook, Instagram, and YouTube. If you’d like to learn which Baumann Skin Type you are and get a customized skincare routine created for you, visit SkinTypeSolutions.com
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