The skin has many functions. Though it is quite flexible it serves as a very stable barrier between your body and environmental insults like moisture, cold and hot temperatures, rays of the sun, and germs and toxic substances.
The skin’s appearance can tell us a lot about a person’s age and state of health. Sometimes a change in the structure of the skin or even change of skin tone and color can be a sign of a medical condition. For example, most of us are aware that yellowish skin indicates a liver condition while very pale skin might indicate that a person’s blood is deficient in red blood cells or that his or her blood is not circulating well.
Even at its thickest point, our skin is only a few millimeters thick. But it is still our heaviest and largest organ, making up about one seventh of our body weight: Depending on your height and body mass, it weighs between … 7.5 and 22 pounds and has a surface area of … 16.15 sq. ft. to 21.50 sq. ft. This goes to show how important skin is for your body and metabolism.” —from “How Does Skin Work?” by InformedHealth.org
Epidermis—The Outermost Layer of Skin
The epidermis is mostly made up of cells that produce keratin—a fibrous protein that forms the main structural constituent of hair, nails, and the outer layer of skin. These are called keratinocytes.
Keratinocytes are gradually pushed to the surface of the skin as newer cells are produced. Here they harden and eventually die off. These hardened keratinocytes, packed closely together, are what seal the skin off from the outside environment.
The epidermis varies in thickness from approximately 0.012 inches thick on the elbows and back of the knees to 0.16 inches thick on the soles of the feet and palms of the hands.
When we lose skin cells in the tiny flakes that fall to the ground as a result of rubbing the skin, the epidermis automatically and constantly is in action to replace these cells by producing more skin cells in its lower layers. The new cells rise to the surface of the skin within about four weeks.
Skin always works to protect itself. It will create a layer of hardened skin called a callus to better withstand pressure and rubbing.
Sometimes but only rarely will sickness or a health condition affect the balance of the shedding of old skin cells and new cell production.*
The epidermis contains other special function cells:
Melanocytes produce and store melanin–a black pigmented cell. Melanin’s function is to protect skin from harmful ultraviolet light from the sun and it’s what causes the skin to tan when in the sun.
Lymphocytes fight germs escorting them to the nearest lymph node.
Merkel cells are what enable us to sense pressure via the skin.
Dermis—The Middle Layer of Skin
Firmly stuck to the epidermis lies the dermis. It’s comprised of a dense network of tough, elastic collagen fibers that serve to make skin strong, healthy, and elastic.
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In various places, the dermis naturally and normally bulges into the connective tissue surrounding the muscles and bones and connects them with the skin.
Capillaries in the dermis carry nutrients and oxygen into the cells while they help the body cool down when it gets too hot. Nerve fibers in the dermis cause it to contain the most sensory cells causing us to quickly react to sensations of extreme heat or cold. The dermis is what allows us to feel sensations of warmth, cold, pressure, itching, and pain.
Subcutis—The Deepest Layer of Skin
The deepest layer of skin called the subcutis is mainly comprised of fat and connective tissue. Tiny cavities in the folds of dermis that bulge into the subcutis store tissue made of fat and water.
The fat acts as both an insulator and shock absorber as it helps to protect bones and joints from shocks, strikes, and bumps. A number of hormones are produced in the fat cells of the subcutis, an example being essential vitamin D** which is produced when the skin is exposed to sunlight.
In addition to containing hair roots, nerves, sweat, sebaceous, and scent glands, both subcutis and dermis contain blood and lymph vessels.
*Conditions affecting the balance of old skin cell shedding and new cell productions include infections, autoimmune disorders or genetic diseases that cause increased growth of rough, scaly skin on the entire body.
**”Vitamin D is actually a hormone rather than a vitamin; it is required to absorb calcium from the gut into the bloodstream. Vitamin D is mostly produced in the skin in response to sunlight and is also absorbed from food eaten (about 10% of vitamin D is absorbed this way) as part of a healthy balanced diet. —“You and Your Hormones,” www.yourhormones.info/hormones/vitamin-d/.
“How Does Skin Work?” InformedHealth.org [Internet]., U.S. National Library of Medicine, 11 Apr. 2019,