Understanding the skin is the first step to understanding how and why to take care of your skin.
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The first step in understanding the skin, is understanding the anatomy of the skin, so let’s dive right in!
The skin is made up of 3 main layers:
Within each of these layers, are sublayers. Let’s break it down layer by layer, shall we?
The Epidermis is the outermost layer of the skin. This is the layer that you can see when you look at your skin.
The purpose of the Epidermis is to give our bodies a barrier and protect us against UV (ultraviolet) radiation, harmful chemicals and pathogens (bacteria, viruses, fungi, etc.), and even protects us from water!
The Epidermis has 4-5 layers, depending on where on the body we’re talking about. Most areas have 4 layers, but areas of thick skin, which include the palms of the hands and soles of the feet, contain a 5th layer. Even though this layer of skin has the most sublayers, it is also the thinnest of the 3 main layers, at around 0.1mm in thickness.
Each layer has a different composition and a different function.
The Stratum Corneum is the outermost layer of the Epidermis, made up of about 20-30 layers of mostly dead, flattened skin cells with no nuclei or cell organelles.
The Stratum Corneum functions as the body’s first line of defense. The name, “corneum” is derived from cornification, also known as keratinization. Cornification occurs in this layer and is the process where living keratinocytes are transformed into dead corneocytes.
The main function of the Stratum Corneum is to help prevent the penetration of of external toxins and bacteria, and other harmful pathogens. The Stratum Corneum also repels water, protects against mechanical stress, such as abrasions that would harm the more delicate, living lower layers of the Epidermis.
The Stratum Lucidum is only found in thicker skin on the palms of the hands and soles of the feet.
This layer is clear, and consists of 2-3 layers of dead, flattened skin cells, similar to the cells in the Stratum Corneum.
The main function of Stratum Lucidum is to give the skin the capability to stretch. The cells in this layer are filled with a protein called eleiden which gives the cells their transparent appearance. The presence of eleiden is what makes the skin waterproof.
The Stratum Granulosum is another relatively thin layer of the skin, with only 3-5 layers of skin cells. The cells in this layer aren’t completely flattened, but have started the flattening process, and therefore have a diamond-like shape to them.
This layer has a granular appearance, hence the name “granulosum”, due to the changes that the keratinocytes are going through.
The main function of the Stratum Granulosum is to act as both a barrier for harmful substances from entering the body, and also a transitional layer where keratinocytes begin to die, causing their nuclei and other organelles to disintegrate, before pushing up to the Stratum Lucidum and eventually the Stratum Corneum.
The Stratum Spinosum is a thicker layer, at 8-10 layers of cells. The cells in this layer have a polyhedral (3 dimensional) shape.
Within the Stratum Spinosum is the beginning of the keratinization process. Keratinization is a process during which epithelial cells (cells that line various structures inside and outside the body, including the skin) become filled with keratin protein filaments. During this process, the cells die and become much tougher and resistant.
The main function of this layer is to help with skin flexibility, and to help the epidermis to withstand the effects of friction and abrasion.
The Stratum Basale, also known as the Stratum Germinativum is the bottom layer of the Epidermis. This deepest layer contains stem cells that create keratinocytes, and also contains melanocytes. This layer is a single layer of cells that are either cuboidal or columnar.
Melanocytes have 2 functions. First, it produces melanin, which gives skin its color. The second function is to protect the living cells in the skin from damage from UV radiation.
The layer beneath the Epidermis is called the Dermis. While the Dermis is only made up of 2 layers rather than the 5 that the Epidermis is made up of, it is much thicker. Though it varies, it is between 1-4 mm.
Within the Dermis are nerves, blood & lymph vessels, hair follicles, sweat glands, and other structures.
The Papillary Dermis is made up of loose connective tissue including Collagen & Elastin, as well as nerve fibers, touch receptors, phagocytes, and lymphatic capillaries. The Collagen and Elastin fibers in this layer form a loose “mesh.” The Papillary Layer is called this because it extends into the Stratum Basale creating finger like projections, known as Papillae.
The Papillary Dermis has 2 main functions.
The reticular layer of the dermis sits below the Papillary Dermis and is thicker. It consists of dense irregular connective tissue. This layer also contains the hair roots, sebaceous glands, sweat glands, and blood vessels.
The main function of the Reticular Dermis is to give the skin strength, elasticity, and structure.
Lastly, the Hypodermis is the bottom layer of the skin, sitting below the Dermis. The Hypodermis is also known as the Subcutaneous Layer, Subcutaneous Tissue or the Subcutis.
The Hypodermis consists of primarily Adiposde (fat) tissue. It also contains fibroblasts, macrophages, loose areolar connective tissue, larger nerves, and blood cells.
The Hypodermis serves 2 main functions:
*Fun fact about the Hypodermis. The thickness of the hypodermis varies throughout the body and from person to person. For example, in men, the hypodermis is thickest in the abdomen and shoulders and ranges from 1.60 mm to 25.45 mm. In women it is thickest in the hips, thighs, and buttocks, and ranges from 3.40 mm to 25.20 mm.
So there you go! Now you have a better understanding about skin anatomy. For more information about skin and how UV light affects the skin, check out this blog post!
Stay tuned for my next post all about what an Esthetician does and what Skin Care actually means!
