Our skin is our identity, we agonize over it, adorn it and spend countless dollars caring for it, but how much do we know about it, and how it actually works?
When we think about protecting ourselves from the elements, our skin may not be the first thing that comes to mind but the skin has multiple vital roles. It is our bodies’ greatest protector against weather, climate, and pathogens. It regulates body temperature, balances hydration and houses the nerve endings that give us our sense of touch. It even synthesizes Vitamin D from UV rays, creating vital nutrients for the body. It is the largest and fastest growing organ of our body, and it’s made up of three main layers; beneath the outermost epidermis lies the dermis, then the hypodermis, but the science behind how it works goes much deeper.
Resilient and tough this outermost layer of our skin is the most protective layer of our body. It’s composed of four main layers, otherwise known as strata. The layers of the epidermis work together in very different and complex ways to regenerate and renew itself, constantly learning to adapt to its environment.
The outermost layer is called the stratum corneum, Latin for “horny layer.” While this layer doesn’t usually feel tough, it does vary in thickness depending on where it is located on the body. For example, the skin on your feet is much thicker than the skin on your chest, face or arms. This layer is composed almost entirely of dead, keratin-filled cells which naturally slough off so often that we end up with a completely new outer layer about every 35 days.
Beneath the stratum corneum is the stratum granulosum, where cells produce a waxy material called lamellar bodies that contain lipids and proteins which aid in waterproofing the skin. It is made up of keratinocytes that have moved up from the stratum spinosum. As these cells move towards the skin’s surface, they flatten and stick together, eventually dying out and sloughing off during regeneration.
Just underneath lies a thick layer of spiny polyhedral keratinocytes called stratum spinosum that helps bond the cells together. Also known as the squamous cell layer, it is composed of basal cells that have matured into squamous cells, or keratinocytes, which produce keratin, the protective protein that makes up hair, nails, and skin.
The stratum spinosum is also home to Langerhans cells which travel from the bone marrow to the squamous layer to work in conjunction with T helper cells to attach themselves to foreign substances that penetrate the skin.
The main job of this layer is to help the skin retain moisture and natural emollients that can keep the epidermis lubricated and resistant to cracking but it is also responsible for synthesizing cytokines, a type of protein that helps regulate the immune response.
The stratum basale is the deepest layer of the epidermis. It contains stem cells which constantly divide, reproducing the skin cells lost in the stratum corneum. The stratum basale is also home to melanocytes that produce melanin, the pigment responsible for skin color. When exposed to sunlight, melanocytes produce more melanin to protect the skin from UV exposure. Abnormalities in the development of these cells can lead to melanoma, the most deadly type of skin cancer.
A fifth layer, called stratum lucidum, is only present on much thicker areas of skin such as the palms of the hands and the soles of the feet.
The epidermis can be impacted by injury, genetics and many external forces that contribute to the aging of the skin such as smoking, alcohol, and excessive UV exposure, all of which contribute to the development of wrinkles, sunspots, and the uneven thickening or thinning of the skin.
Non-melanoma and melanoma skin cancers originate in the epidermis. This outer layer of skin is also where rashes and blisters appear, caused by everything from infections and allergies to diseases and toxins.
Infiltration of the epidermis can cause infections the body could otherwise defend against, such as diseases caused by insect or animal bites, as well as pathogens that enter the body through cuts sores, and abrasions.
Underneath the epidermis lies the dermis. This middle layer contains blood vessels, hair follicles, lymph vessels and the glands that produce sweat, which helps regulate body temperature. It’s also responsible for the production of sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin's surface through tiny openings in the skin that act as pores. The dermis itself is made up of two layers, the papillary dermis, and the reticular dermis. Its primary purpose is to support the epidermis and help the skin to thrive but it has a number of other functions as well.
The papillary dermis is made up of capillaries, elastic fibers, reticular fibers, and collagen, which make up 70% of the weight of the dermis. These vascular networks serve two essential functions; first it provides the epidermis with vital nutrients and secondly, it supplies the body with thermoregulation. The capillaries remove oxygen-depleted blood from the skin to allow entry of fresh blood.
This layer of the dermis also consists of free sensory nerve endings that sense high temperatures and other dangers, sending chemical and electrical messages telling the brain to react.
The reticular layer of the dermis is thicker than the papillary dermis. It is made up of dense irregular connective tissue which strengthens the skin; giving it overall structure, strength, and elasticity. This layer supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.
The innermost layer is the hypodermis, a layer of subcutaneous fat and collagen cells that lies between the dermis and the underlying tissues and organs. Also known as the subcutis, this layer is primarily comprised of adipocytes; cells dedicated to storing fat. This provides the body with energy, in addition to thermal insulation while absorbing the shock from impacts to the body.
The thickness of the hypodermis varies throughout the body and from person to person. Men have a thicker hypodermis than women, and in both sexes, the thickness of the subcutis layer thins with age.
Just as the hypodermis stores fat, it also provides good storage space for drugs that need to be released into the body gradually. The subcutaneous tissue is a route of administration for drugs such as insulin; because it is highly vascular, the tissue absorbs drugs quickly. Subcutaneous injection is believed to be the most effective manner to administer some drugs, such as human growth hormones.
The team at BioElementis does the research to keep you informed about the latest in skincare and the science behind how it works. Do you have questions? We'll find the answers!