In order to understand acne, and how it arises, I think it’s helpful to have a quick understanding of the skin.
There are 3 layers that make up our skin.
The deepest layer is the Subcutaneous Fat. This is, as it sounds, a fat layer that provides cushioning between the top layers of the skin and the muscle and bone that lie underneath. Larger blood vessels and lymph vessels travel throughout this space. It also helps control our body temperature, making sure we don’t get too warm or cold. (1)
The second and middle layer is called the Dermis. The dermis is home to many important skin components, including collagen, elastin, blood vessels, nerves, hair follicles, and glands.
Collagen and elastin form the fibrous (firmness) and bouncy (snap-back) components of our skin. Collagen is particularly rich here, making up about 75% of the dermis in dry weight (6). We attribute an abundant presence of both of these with health and youthfulness of the skin. They interweave within a jelly-like material called the “ground substance,” which, along with fat, helps surround and cushion the vessels, follicles, and nerves present here.
Hair follicles form in the deepest layers of the dermis where they are supplied by blood vessels and nerves. These hair follicles travel up through the dermis and top-most layer (epidermis) of the skin where they eventually open at the surface and form what we see as pores.
There are 3 types of hair follicles, but the one we’ll focus on is the sebaceous follicle, as this is where acne occurs.
Sebaceous glands are found mid-dermis and are almost always attached to a hair follicle (3). These glands secrete oil which is used to moisturize the surface of the skin and form a protective layer. There are 800 sebaceous glands per centimeter of skin on the face in comparison to an arm or leg, where less than 50 glands per square centimeter are seen. Sebaceous glands are present everywhere except for the palms of the hands and soles of the feet. However, facial sebaceous glands are considerably larger than those noted elsewhere. (2)
As an added note, the sebaceous gland is under hormonal control – specifically the male androgen hormones. Androgen Receptors are present in numerous skin components, with a particular preference for the sebaceous gland, where androgens stimulate cell proliferation and oil production. (4)
“In acne patients, there is a direct correlation between the amount of sebum produced by the skin of an individual, and the severity of the acne. The more sebum produced, the worse the degree of acne. Controlling sebum production in acne patients definitely helps improve acne conditions” (2).
The uppermost layer of the skin is the Epidermis. Funnily enough, there is only one layer of the epidermis considered alive, and this sits at the bottom of the epidermis just above the dermis. This layer duplicates itself to form new cells, which move up through the epidermis to the very top, forming the outermost layer that we see and think of as the skin. These eventually exfoliate or fall off, and the cycle continues. The skin regenerates itself approximately once every 28 days.
Now the walls inside the sebaceous follicle (the hair follicle responsible for acne) also follow a pattern of regeneration. However, while the top most layers of the follicle act very similarly to that of the epidermis, the deeper layers act differently. They shed very quicky and are not as formed as those at the top. Because of the constant quick shedding of these lower cells, the canal of the sebaceous follicle can constantly be full of lose, dead cells. (2)
In “normal” skin, these cells continuously shed and are exfoliated away. But in acne-prone skin, the cells build up within the sebaceous follicle and can form a plug (otherwise known as a microcomedo, which we cannot see). The accumulation of these cells is called retention hyperkeratosis. When the follicle opening is blocked, it prevents the exit of the sebaceous oil, and the combination of the skin cell buildup with excess oil can lead to the development of acne.
This is a very basic understanding of how acne can form, and there are many factors that contribute to sebum production and skin cell build up. However, I would be amiss if I didn’t mention the bacteria that live within our skin; the bacteria that thrives on lack of oxygen and sebaceous oil.
Proprionibacterium acnes (P. acnes) is a bacterium that is a major resident of the normal human skin microbiome and dominates the sebaceous follicles. P. acnes is found in both non-acne and acne-prone skin types, and it is “believed to play an important role in maintaining skin health (5).”
P. acnes cannot survive in the presence of oxygen. In normal skin, where skin cell blockades do not occur, the P. acnes is kept in check by the presence of oxygen into the pore. But in acne-prone skin, this buildup plug keeps oxygen out, and P. acnes is able to flourish. P. acnes’ metabolic process ultimately leads to inflammation of the sebaceous follicle wall, causing the walls to breakdown and eventually rupture. As the walls rupture, the debris, including p. acnes bacteria, spill out into the dermis. (2)
When our immune pulls up to the site of the rupture, white blood cells and more enzymes are released that increase the already inflamed site. This can lead to worsening swelling, discomfort, and acne lesions.
These four things represent the pathogenesis of acne:
(1) male hormone induced sebaceous gland activity
(2) retention hyperkeratosis
(3) proliferation of P. Acnes
(4) immune reaction response to any and all noted above
And there you have it. Acne is multifactorial, meaning a combination of things play a role in its development. Skin care, oral care, hair care, body care, stress, diet, and lifestyle all play a role in the development of acne. It’s all connected. It’s a cohesive system. And by diving into all of these avenues, you can find your own path to your best, healthiest skin.
Subcutaneous Fat: What You Need to Know About the Fat Beneath Your Skin. (2022, August 7). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/23968-subcutaneous-fat
Lees, M. (2014). Clearing Concepts : A Guide to Acne Treatment. Milady.
Cleveland Clinic. (n.d.). Sebaceous Glands: Function, Location & Secretion. Cleveland Clinic. https://my.clevelandclinic.org/health/body/24538-sebaceous-glands
Hoover, E., Aslam, S., & Krishnamurthy, K. (2022). Physiology, Sebaceous Glands. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK499819/#:~:text=Sebaceous%20glands%20 are%20located%20in
McLaughlin, J., Watterson, S., Layton, A. M., Bjourson, A. J., Barnard, E., & McDowell, A. (2019). Propionibacterium acnes and Acne Vulgaris: New Insights from the Integration of Population Genetic, Multi-Omic, Biochemical and Host-Microbe Studies. Microorganisms, 7(5), 128. https://doi.org/10.3390/microorganisms7050128
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