Hi Patrons, and welcome back to the blog. 🙂
I hope you have something fun or at least restful planned for the weekend. I will be sleeping in and trying to decompress from arguably a long week. I also have a tube of Differin (adapalene, a synthetic retinoid) coming in tomorrow (Saturday) so hurrah! I am excited to try it again. Back when I first used Differin, my skin was hella irritated and did not appreciate it. I do have some texture issues on my forehead and chin I’d like to clear up though (as well as sporadic breakouts, since these are the original and only areas I’ve ever really dealt with acne), so I might chronicle my journey with Differin for you all if you’re interested.
Also I apologize that this wasn’t put out sooner – I had a tomato plant emergency (don’t ask) and the DMV took three hours.
So yesterday, I took you through the glands of the skin, and then last night, I was reading a 2009 study on acne that was really interesting and I wanted to share it with you all!
In parallel, research into the functions of the sebaceous gland has yielded exciting information about the central role these glands play in regulation of skin functions. The sebaceous gland regulates independent endocrine functions of the skin and has a significant role in hormonally induced aging of skin. In addition, the sebaceous gland has both direct and indirect antibacterial activities. Sapienicacid, a lipid in sebum, has innate antimicrobial activity and is up-regulated by activation of TLR-2 by skin bacteria. Further, the sebaceous gland has ubiquitous expression of antibacterial peptides and proinflammatory cytokines/chemokines; these substances are induced in sebocytes by the presence of bacteria. The sebaceous gland acts as an independent endocrine organ in response to changes in androgens and hormones, and is the control center for a complex regulatory neuropep-tide program that acts like the hypothalamus-pituitary-adrenal axis. This aspect of sebaceous gland function is primarily influenced by corticotrophin-releasing hormone, its binding protein, and corticotrophin receptors. Corticotrophin-releasing hormone levels change in response to stress, and its role in regulating sebaceous gland function is likely a link in the brain-skin connection that is thought to explain the relationship between stress and skin disorders with an inflammatory component such as acne. Similarly, substance P, a -melanocyte-stimulating hormone, and corticotrophin-releasing hormone-receptor-1 are involved in regulating sebocyte activity. … The response of skin to stress is a subject of active investigation and may soon suggest new targets for therapeutic interventions. (Source)
So from that:
- The sebaceous gland is a neuro-endocrine inflammatory organ that likely creates local responses to stress (hence why you break out during periods of extreme stress)
- Androgens have influence on follicular corneocytes (explaining why women tend to have more issues with acne through life and why birth control or androgen-suppressants like spironolactone helps)
- Oxidized lipids in sebum can stimulate inflammation in skin (meaning exposure to pollution in the air and/or UV oxidizes sebum and inflames skin)
- Oxidized sebum combined with inflammation ages skin prematurely
Alright, I’ll get on with it, but I just had to share that because I thought it was really interesting!
The skin is a highly-specialized set of tissues that is divided into three parts, with connective matrixes between. These three parts are the epidermis, dermis, and hypodermis, which is also known as the subcutaneous layer.
There are many different types of cells in the skin, but the most important are keratinocytes, melaninocytes, fibroblasts, and the immune cells such as Langerhans, mononuclear cells, and mast cells.
The connective networks in between are known as the extra cellular matrix or the ECM. These networks contain the cells primarily responsible for skin suppleness, elasticity, and flexibility. A surprisingly complex network, it regulates important functions like hydration, temperature, and permeability and acts as the glue that holds everything together.
Each cell also is covered with a membrane with receptors which perform what is called “cell signalling.” These receptors allow cells to bind with various chemical components that pass between cells or communicate with ingredients such as tretinoin (brand name Retin-A), adapalene (Differin), or Taz (tazarotene). That is how and why Retin-A can be credited with increasing cell-turnover and is literally called a “cell-communicating ingredient.”
The epidermis is what is visible to your eyes and what we most commonly think of as our skin. It is only 25 to 30 cells deep, which amounts to roughly 1.6mm on the thickest parts (feet) and .04mm on the thinnest parts (eyelids). It is surprisingly complex despite being so thin, composed of keratinocytes, which are constantly reproducing in the deepest layer of the epidermis (stratum basale); Langerhans cells which remove antigens from the skin to the lymphatic system; melanocytes which provide the color of the skin; and Merkel cells, which govern the sense of touch.
The second layer of skin is the dermis. It lies beneath the epidermis and is connected through an intercellular membrane. At it’s thickest, it is 3mm (on the back) and .3mm at it’s thinnest (on the eyelids). It is composed of the glands of the skin (sweat and oil), collagen and elastin connective tissues, blood vessels, and nerves.
The third layer, the hypodermis, is the deepest layer and consists primarily of fat, connective tissue, large blood vessels, and nerves. It is important for regulating body temperature as well as skin temperature.
The epidermis is perhaps the most important layer of the skin and understanding the epidermis allows us to understand product penetration and efficacy. It is the layer most affected by UV, inflammation, skin diseases, cigarette smoke and cigarette smoking, as well as skin cancer.
It is one of the most metabolically active layers of skin, synthesizing lipids and containing what is needed to form the lipid layer. It is the layer that houses the most free radical scavengers such as vitamin E and C, and contains large amounts of natural ceramides as well as glycosaminoglycans.
It is broken down into four distinct layers:
- Stratum corneum (SC)
- Stratum granulosum (SG)
- Stratum spinosum (SS)
- Stratum basale (SB)
The stratum corneum is the thickest, outermost layer. Flattened keratinocytes (corneocytes) or “dead cells” have no nuclei, though they do retain some of their metabolic and signalling functions. They are abundant in keratin, which they gain on their progression from deep within the SB to the very top SC. This layer also contains only 10-15% water, which is held in the cell’s cytoplasmic gel and intercellular channels (spaces between cells). The younger you are, the more water is present. As we age, the skin’s ability to hold onto water decreases. They serve to protect the skin from water loss as well as injury. As skin gets pushed upwards, it results in the sloughing of these surface “scales,” known as desquamation.
The Langerhans cells are also found in the epidermis. They are typically found in the lower layers of the epidermis and comprise roughly 5% of the total epidermal cell population. These cells carry antigens from the epidermis to the lymphatic system to be eliminated. They are also the cells most sensitive and susceptible to damage from UV rays. Even small amounts of UV (<10 minutes of exposure) can result in damage to the Langerhans cells, which inhibits the skin’s entire immune response. As we age, we lose Langerhans cells, which may be why skin diseases and skin cancers increase with age.
When we are young, it takes roughly 28 days for a cell to travel from the SB to the SC. This process plummets as we age, dropping to roughly 37 days at age 50. Products like Retin-A are designed to speed this process up by communicating with the cells.
In the deepest layer of the skin, the SB, is where cells reproduce through mitosis (one cell dividing into two). One cell remains in the SB and another travels upward, to the surface of the SC. As the cells migrate, they secrete lipids that create cohesion between the cells and help the epidermis hold moisture. This is why it is so crucial to consider the appropriate products to use on your skin, as it is what maintains this health.
The skin’s exfoliation process is controlled through enzymes. These enzymes break down, allowing the skin cells to be shed. However, if this process is not working as it should, skin cells accumulate, causing hyperkeratosis (many skin conditions are conditions of hyperkeratosis, such as keratosis pilaris forms, for example).
The SC also contains a layer of natural moisturizing factors (NMF), which are hydrosoluable (able to dissolve in water) and hygroscopic (able to retain water) substances that regulate the permeability of the SC. Harsh soaps wash away the NMF, rendering skin fragile and dry.
Skin pigmentation is also formed at the deepest layer of the epidermis. Excessive melanin production can be caused by sun/UV exposure (getting a tan), hormonal imbalances (melasma), or trauma to the skin (post-inflammatory hyperpigmentation). In the case of UV exposure, melanocytes rush to create melanin in an attempt to protect the skin from UV damage.
Touch is controlled by the Merkel cells, which are modified epidermal cells with a receptor. They are named after the scientist, Friedrish Sigmund Merkel, who first described them.
Together, melanocytes, Merkel cells, and Langerhans cells account for 13-20% of the total epidermal cells.
The second layer of skin, it is about 10-40x thicker than the epidermis. It houses the hair follicles, sebaceous glands, and the two types of sweat glands as well as capillaries and nerves.
The dermis is perhaps best known for the housing of collagen and elastin, which makes up roughly 70% of dermal proteins and holds the water found in the dermis. Collagen is also responsible for wound healing by producing very thin collagen fibers are which gain thickness (I like to think of them like the strands of muscle being built on Hosts in Westworld). The dermis is made of a network of other fibers that are responsible for hydration, resistance to pressure, and orientation of other proteins.
Collagen in the dermis also acts as a structural support system that holds the nerves, glands, and blood vessels in this layer while providing the skin with strength and elasticity. Its production begins with procollagen, which goes through a series of changes to become regular collagen. Procollagen decreases over time, which is why skin gets drier, wrinkles, and loses elasticity as a person ages.
In undamaged skin, collagen and elastin fibers make up for 2-4% of the dermis.
The hypodermis or the subcutaneous layer is the last layer of skin, tucked just below the dermis. This is what gives skin its shape and acts as a thermal insulator, shock absorber, and nutritional depot. Attached firmly to the lower surface of the dermis, it glides fairly smoothly over deeper fascia, giving skin mobility. The fat of the tissue protects nerves and other underlying tissue. It is not present in the thinnest parts of the skin, such as the eyelids.