Gut Microbiome and Gut-Skin Axis

Did you know that we have about as many bacteria in, and on, our bodies as we have cells?^[1] Some of the most compelling research of the past decade investigates the gut microbiome, or bacterial environment of the gut, and its relationship to various health conditions. Many notable relationships between gut health and the health of other organs have emerged, including the relationship between the gut and the immune system.^[2] This discovery sheds light on how improving gut health may improve the health of our skin. So how exactly does this work?

Gut Homeostasis and the Gut-Skin Axis 

Lining the gut, especially the large intestine, are billions of bacteria that ferment our food as a natural part of digestion. These bacteria appear to play significant roles not only in gastrointestinal health but also in various other organs - such as the skin.^[3] This relationship between the gut and skin is often referred to as the “gut-skin axis.” Clinically, practitioners see that many gut pathologies have skin co-morbidities.^[3] Several theories have surfaced as to why this occurs. One particular theory claims that metabolites, or break-down products, from the diet and gut bacteria, somehow become skin accessible.^[3]

When the microbiota of the gut are lacking or functioning inappropriately, certain issues can arise. It is important that we have the growth of specific strains of bacteria in order to maintain health and proper digestion. The bacteria that live and divide along the gut regulate and protect the epithelial lining of the gut tissue, acting as part of the barrier against outside foreign particles.^[2] This protection is a major mechanism for the body to eradicate potentially harmful invaders such as unwanted bacterial or other organisms. The epithelial cells lining the gut wall produce mucus, antimicrobial peptides, and proteins to facilitate the capture and destruction of foreign invaders.^[2] These functions are part of our “innate immune response.”

When the gut homeostasis is altered, increased inflammatory signaling, increased gut lining permeability, and abnormal growth of gut bacteria, known as dysbiosis, can result.^[2] Unsurprisingly, these changes often lead to gastrointestinal symptoms and disorders. Clinicians are exploring more about increased gut permeability, which is often referred to as “leaky gut syndrome.”

Gut Health and Skin Conditions 

More and more, clinicians and researchers recognize the correlations between the gut microbiota and different skin conditions. For example, one birth cohort study shows that a decrease in gut bacteria diversity in infants correlated to developing atopic dermatitis (eczema) later in life.^[4] A later study in adults with eczema showed no change in overall bacterial diversity, but there was an enrichment of Faecalibacterium prausnitzii in people with atopic dermatitis, suggesting that there are still observable changes in the gut microbiome between those with and without atopic dermatitis.^[5] Another cross-sectional study assessing patients with systemic sclerosis (a condition where the skin and other organs thicken and become replaced with scar-like tissue) found that intestinal dysbiosis was common among this population and was associated with both gastrointestinal and skin symptoms.^[6]

A third example includes a randomized, double-blind, placebo-controlled pilot study whereby researchers administered probiotic supplements to adults with acne.^[7] The study results showed that those taking probiotic supplements of the Lactobacillus rhamnosus SP1 (LSP1) strain for 12 weeks showed improvements in the appearance of their acne, compared to those taking placebos.^[7] The authors suggest that this result is due to the normalized gene expression for genes involved in insulin signaling in the skin of subjects on probiotic treatment.^[7] This study advances support for addressing the gut microbiome as a part of treating skin conditions.

Overall, studies assessing the "gut-skin axis" in various skin conditions are emerging with more studies on the horizon. What seems promising is that a flourishing and diverse gut microbial population may support skin health.^[2,4,6,7] Much more research is warranted for this topic, as it may yield evidence for changes to how dermatology is viewed in the context of the gut microbiome. Until then, strive for optimal gut health - your skin will thank you.