By Dr. Anna Gold
In my new Skin Series blog posts, I go deep into internal factors that contribute to the health of skin, including the role of the microbiome, a Chinese medicine perspective, and diet and lifestyle habits that help its complexion.
To start, Let's go over the structure and function of the skin, which is fundamental to understanding the importance of nourishing the skin from the inside out. Some people falsely believe that the only way to care for their skin is to lather products on top. What they may not realize is that although the quality of topical ingredients in skincare are important for healthy skin, how they care for the body holistically is just as important.
First, here’s a primer on the biology of skin...
The Basics: Structure and Function of Skin
Being the largest organ of the body, the skin has functions which are often ignored until something goes wrong. When you get a paper cut, a pimple, or sunburn you’re reminded of how extraordinary your skin is. It protects you from the elements, forming a seal to fend off the outside world. It protects you from bacteria, pollution, and temperature fluctuations. Skin contains vital chemicals and nutrients in the body, and processes sunlight into vitamin D, transporting this essential vitamin to support immunity and bones. The connection between the skin and the internal organs is evident in changing skin color and textures. When internal organs are sick, the color and texture of the skin will oftentimes change. Changes in the skin can provide clues to systemic diseases.
The average adult’s skin measures 2 m² (6.5 square feet) and weighs about 10 pounds. The skin is made up of three major layers: the epidermis, dermis and the subcutaneous layer, also called the fat layer.
The epidermis is the outermost layer of the skin, which itself is made up of five layers. It consists mostly of keratinocytes.They are made up of cells that come from the deepest layer of the epidermis which slowly migrate upwards towards the surface, becoming the outermost layer of the skin with which we come into contact. When the keratinocytes reach the superficial layer, they are gradually shed and replaced by newer cells. This constant process of cell turnover takes on average 28 days, often longer for people who are older.
The epidermis is where the skin microbiome resides. It hosts about 1 trillion bacteria, fungi, yeast and viruses, which play a role in maintaining healthy resilient skin. This is where the immunity of the skin is most active.
Within the epidermis itself are five layers. Starting from the deepest to the most superficial layer, the epidermis consists of:
- The Basal layer (Stratum Basale) - where skin cells originate. This is the layer where melanocytes which are the cells that determines the color of the skin
- The Prickle layer (Stratum Spinosum) - where the cells become irregular in shape and begin interlocking in a rigid tough structure
- The Granular layer (Stratum Granulosum) - where the cells from the deeper layers begin to flatten and become the waterproofing protein keratin. The keratinocytes in this layer is where the membranes consisting of lipids, enzymes and proteins form. This is the portion that is essential to the barrier function. It is in this layer where the nuclei and organelles within the cell start to disappear and the cells left over start becoming the tougher protective layer of the skin.
- The Clear layer (Stratum Lucidum) is only found in areas continuously being rubbed such as the palm of the hands and the soles of the feet. The cells produce a substance called Eleidin that helps cushioning and absorbs friction.
- The Cornified layer (Stratum Corneum) is the hardened dead layer of the epidermis that is the outermost portion of the skin. It’s the exposed part of the skin that provides a tough barrier against the physical onslaught of weather and pathogens.
The dermis is composed of connective tissue such as collagen, elastin, reticular fibers that provide the skin with stability and elasticity. It is where the blood and lymphatic vessels, nerves and sensory receptors, as well as the hair follicles, sweat and sebaceous glands reside.
The hypodermis, or subcutaneous tissue layer, is where the fat and loose connective tissues live.
Now that we've established the anatomy of the skin, head to the next blog post for a TCM perspective.
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