What is the skin, really?
The skin is the largest organ in the human body. It weighs approximately 25 pounds in the average adult human, and it is the fundamental primary boundary of our immune system. It’s a wall that keeps water, debris, bacteria, and even radiation from the sun out of our finely tuned biological system. Our skin has evolved over millions of years to be durable but flexible, absorbent but not porous, and most importantly strong enough to withstand a century of wear and tear. It’s separated into three distinct layers that each perform a specific role.
The epidermis is the part of the skin that you can see; it’s your first line of defense. It’s made up of waterproofing cells that serve as a physical barrier to infection, pressure-sensing nerves, melanin-producing cells that determine the pigmentation of your skin, and immune cells which copy bacteria on your skin that will never enter your body to help you prepare defenses just in case they enter through a cut or a mucous membrane.
This is the thickest layer of skin. It’s home to your hair follicles, sweat glands, sebaceous glands, and most of the nerve cells that provide us with a physical map of the world around us. It is comprised mostly of collagen, reticular fibers, and elastic tissue that gives it its flexible strength. In addition to sensory nerves, there are also efferent (control rather than sense) neurons that govern capillary dilation and lymph networks that help to protect our body from any infection that may occur in the skin. The oil that covers our skin, called sebum, is produced by sebaceous glands in this layer of the skin as well.
This is the deepest layer of the skin, and this is what gets exposed when you have a blister. It is home to yet more immune system tissue, sensory receptors, and adipocytes (fat cells) that provide insulation from external temperatures, padding from physical injury, and storage of our biological fuel. In fact, the skin contains roughly half of body fat.
Endocannabinoid involvement in the skin
The endocannabinoid system is the sum of all of the cannabinoid receptors, endogenous ligands (like anandamide) that bind to them, their biosynthetic pathways, and degrading enzymes. But the effects of this system, both acute and long term, are much deeper than just some ligand binding with a receptor. Its discovery and research since the early 1990s have provided much insight into previously misunderstood mechanisms in the body, namely homeostasis.
To that end, the overwhelming majority of conditions described in anecdotal evidence as responding positively to phytocannabinoid treatment (plant cannabinoids such as CBD) are homeostasis-related, and they usually have no known cause or cure. For that reason, endocannabinoid modulation has proven to be a highly effective method of treatment for many diverse conditions.
Skin and hair growth
In the skin, one of the better-understood roles of the ECS is in the production of hair. Hair follicles and the sebaceous glands that accompany them have a high percentage of CB1 receptors. These are responsive to the endocannabinoid AEA (anandamide) and to phytocannabinoids like THC and CBC. Hair growth shows a negative correlation with activation of these receptors, so scientists believe that the ECS controls human hair growth via a negative feedback loop. This process is undefined as yet, so an ECS explanation is very reasonable.
We know the ECS plays a very intricate and sophisticated role in the immune system. The precise mechanisms of its various roles are not well documented however. It is known that it up- and down-regulates the overall level of cellular activity in immune cells, and it also regulates the rate at which apoptosis, or programmed cell death, occurs. This is a vital function of the skin.
The skin also is prone to inflammation and allergic reactions because it is often the first to come in contact with foreign substances. The ECS plays a very robust role in the down-regulation of chemokines and cytokines that produce inflammation and the pain associated with it. Indeed, localized topical cannabinoid treatment of allergy-induced inflammatory responses (putting CBD on hives) attenuated the symptoms of inflammation immediately, in a CB1 dependent manner, proving that cannabinoid receptors are involved in the negative feedback of painful inflammatory responses.