Microbiome Living on Your Skin

The Scope:

You already know the verdict on the skin, in term of its structure, and functions. This script examines the importance of bacteria living on your skin as a contributor to good skin health. We will focus only on skin bacteria, then move on to gut bacteria.  Even though we can't see them, these creatures live heavily on our skin. Each region on the skin such as your elbows, groins, shins, and hands can all be considered separate boroughs. For example, on average the skin houses a range of 103 to 104 colony forming unit/cm2 (CFU/m2) of bacteria. CFU is essentially the count of clusters of bacteria in a sample. For this purpose, a sample of skin contains an abundance amount of these species. The epidermis and dermis are full of bacteria. It’s insane! Each borough is characterized by a unique demographic, environment, and culture norms that influence the quality of our skin. Most humid places like the groins, and armpits tend to surpass 106 CFU while the upper back and arms are slightly above the average CFU. To maintain healthy skin, it is necessary to maintain a balanced microbiome. When our microbiome is out of balance, we are more likely to develop skin issues. 

Let's explore the role that a healthy bacterial population plays in skin health.    

Given that the skin is the largest organ of the body, there are a lot of bacteria living there! Our microbiome is composed of bacteria, fungi, viruses, dust mites, archea, and phages. Like the skin, internal and external variables influence the microbiome. Extrinsic factors affecting the skin microbiome are listed below:

• hygiene

• beauty routine

• exposure to chemicals

• availability of nutrients for microorganisms

• sunlight

• climate

• physical activity

• air and water pollution

In general, 90% of human skin microbial population are characterized into four categories:

1. Antinobacteria (52%)

2. Firmicutes (24%)

3. Proteobacteria (16%)

4. Bacteroidetes (6%)

Staphylococcus epidermidis, Corynebacterium, Micrococus, Streptococcus and Acinetobacter are the most common species in these categories. In contrast to other species, Staphylococcus, Cutibacterium acnes, and Corynebacterium are abundant throughout the skin. It is most common for fungi to reside on the foot, such as Aspergillus and Crytococcus. On the skin, viruses are scarce since the large bacterial population occupying the epidermis crowds them out. Microbiomes also change as we age; some relocate to other parts of our skin to accommodate us and keep our health intact. Firmicutes dominate the facial area during childhood, while Proteorbacteria dominate the adult face. However, Proteobacteria are the dominant microbial type on the hands throughout life. In general, as people age, microbial diversity decreases, and microbial organization becomes more monocropping. The way we are designed makes us susceptible to certain bacteria, which might not be appropriate for each of us depending on our age, immunity, or genetics. Streptococcus, for instance, is beneficial to children's skin but harmful to elderly skin. 

It's likely that you are saying that these microbes benefit from us right now. Hang on, buddy. We provide shelter, but they don't live on your skin for free. Countless skin microbes are commensal, which means we benefit from them while they benefit us. Consider tree frogs that use plants for protection. Our commensal friends let their actions speak for themselves and that is how they show their gratitude to you.

The microbiome works closely with your immune cells and keratinized skin cells to maintain a healthy immune system in the skin. Here’s a short list:

1. Microbes heavily occupying your skin prevents the development of pathogens

2. Strains like S. epidermidis create enzymes and use their unique alpha helical shape to attack and eradicate pathogens

3. A variety of Staphylococcus epidermidis species produce an antimicrobial lipid-protein compound to fight infection

4. S. epidermidis create a certain cell wall polymer known as lipoteichoic acid that reduces skin inflammation

5. Cutibacterium acnes makes enzymes that break down lipids in their most basic form to release free fatty acids in sebum (location where oil is released) that alter the skin surface, making it inhospitable for pathogens to establish themselves.

All the above is ideal when a person's health is optimal. Having the right microbes on the skin facilitates proper skin function, as I mentioned earlier. Once unwanted visitors claim turf and buy out property to drive out the healthy bacteria, this imbalance triggers skin issues. Acne, psoriasis, and atopic dermatitis are diseases related to disturbed skin microbiomes. For the development of psoriasis, streptococcus and staphylococcus abundance are crucial. In the coming weeks, we will discuss how to help keep your microbiome healthy. Our next exploration will consider the gut microbiome and its impact on skin health. I’ll catch you on the flip, Stay Strong & Stay Vivid!                             

Fun Fact:  Your puppy sheds fur, you think. The average adult sheds 600,000 to 1.0 million cells per hour. Because exfoliate cells like the keratinized skin cell contain bacteria, they affect the microbial composition. Since the outer layer of the skin releases keratinized skin cells every four weeks, this process leads to skin renewal.   

Reference:

1.  Skowron. K. et al. (2021). Human Skin Microbiome: Impact of Intrinsic and Extrinsic Factors on Skin Microbiota. MDPI. https://doi.org/10.3390/microorganisms9030543.

2. Ratanapokasatit. Y. et al. (2022). How Microbiomes Affect Skin Aging: The Updated Evidence and Current Perspectives. MDPI. https://doi.org/10.3390/life12070936.

3. De Pessemier. B. et al. (2021). Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions. MDPI. https://doi.org/10.3390/microorganisms9020353.