Skin Microbiome Composition and Function

Human skin is home to many types of bacteria, fungi, and viruses that compose the skin microbiota or microbiome. As with microorganisms in the gut, these organisms have an important role in protecting from pathogens and breaking down natural products.¹ The sheer quantity of life found in the skin microbiome is staggering. It often contains up to one billion microorganisms on a single square centimeter.² To protect from pathogens, the skin microbiome forms a physical barrier, and when there is a break in the barrier or the microbial balance is disturbed, it can induce skin or systemic disease.¹ The composition of microbial organisms found in the skin microbiome depends on the physiology of the skin site, with moist, dry, or sebaceous conditions impacting the number and type of microorganisms present. Changes in the abundance of organisms are associated with moist, dry, and sebaceous conditions.¹

How much do you know about skin management? Take our 10-question quiz to find out! Click here.

Bacteria are the most prevalent microorganisms across all sites of the body, whereas fungi are the least. Certain bacteria, such as Staphylococcus and Corynebacterium, thrive in humid and moist environments, such as the feet and bends of the elbows. Fungi of the genus Malassezia are found across all areas of the core body and arms, whereas the feet generally contain Malassezia, Aspergillus, Cryptococcus, Rhodotorula, and others. Unlike with bacteria and fungi, colonization by eukaryotic DNA is specific to the individual rather than each anatomical site.¹ Recent research has discovered evidence that extensive communication occurs among bacteria, skin cells, and immune cells to reinforce and repair the microbiome barrier. These actions increase the body’s defense against infection and can reduce inflammation.³

Factors Affecting the Skin Microbiome

Both the assembly and the equilibrium of the human microbiome are influenced by intrinsic and extrinsic factors. Daily actions, such as touching, eating, and bathing, can alter its composition. The microbiome demonstrates resistance to change and is somewhat able to recover its original composition after it has been altered. Additionally, it is crucial to understand that the microbiome environment is constantly exposed to external factors, and certain conditions can permanently alter its state or structure. It is also continuously influenced by chemical, biological, and physical factors that can impact its stability and composition.⁴

Maintaining a Moisture Balance for the Microbiome

The skin is naturally acidic, with a pH of 4.5 to 5.5, and it is generally cool,⁵ desiccated, sparse in nutrient availability, and salt rich. These traits make it a poor habitat for bacterial growth overall. However, there are areas where the skin’s properties, including temperature, moisture, pH, and oxygen availability, contribute to different microclimates.⁴ The health and balance of the microbiome rely on balancing all of these elements. Skin microbiome features change according to lifestyle and age. Moisture levels are especially susceptible to change. Older patients and those who are bedridden may experience skin deterioration related to urine and fecal incontinence, which can lead to a greater abundance of pathogenic skin microorganisms. On the other end of the spectrum, if the skin becomes dry and desiccated, it is more fragile and susceptible to injury. This is amplified by the fact that as we age, less and less collagen is deposited into the skin, consequently rendering the skin thinner and more fragile.⁶

Conclusions

Managing moisture is essential to promote a healthy microbiome. Appropriate moisture management helps protect the integrity of the microbiome’s protective barrier function. When moisture is balanced and the microbiome is healthy, it can⁷:

• Prevent infection
• Reduce inflammation
• Protect from environmental aggressors, such as ultraviolet rays

Managing moisture is especially important for wounded or delicate skin. Too much moisture compromises the integrity of the microbiome, and it not only leads to skin damage, but also provides a portal of entry for pathogens. Additionally, excessive moisture can optimize conditions for bacterial proliferation on wounds, thus leading to inflammation or infection and prolonging the healing process.⁸

References

1. Byrd AL, Belkaid Y, Segre JA. The human skin microbiome. Nat Rev Microbiol. 2018;16:143-155.
2. Weyrich LS, Dixit S, Farrer AG, Cooper AJ, Cooper AJ. The skin microbiome: associations between altered microbial communities and disease. Australas J Dermatol. 2015;56:268-274.
3. Eisenstein M. The skin microbiome. Nature. 2020;588, S209. https://www.nature.com/articles/d41586-020-03523-7. Accessed March 26, 2021.
4. Moskovicz V, Gross A, Mizrahi B. Extrinsic factors shaping the skin microbiome. Microorganisma. 2020;8:1023-1040.
5. Proksch E. pH in nature, humans and skin. J Dermatol. 2018;45:1044-1052. doi:10.1111/1346-8138.14489
6. Kirkland-Jyhn H, Zaratkiewicz S, Teleten O, Young H. Caring for aging skin. Am J Nurs. 2018;118(2):60-63. doi:10.1097/01.NAJ.0000530249. 91452.4e
7. Fitzgerald K. Skin microbiome 101: how to nurture good bacteria & glowing skin. Mbglifestyle. 2020. https://www.mindbodygreen.com/0-23996/your-skin-microbiome-why-its-esse…. Accessed March 26, 2021.
8. Woo KY, Beeckman D, Chakravarthy D. Management of moisture-associated skin damage: a scoping review. Adv Skin Wound Care. 2017;30(11):494-501.