Gut-Skin axis, skin barrier function

Graphic courtesy of Trompette et al 2023 and Creative Commons license

Many ladies (and the occasional male) engage in elaborate skin routines every day to maintain the appearance of smooth, moist, healthy skin. It’s not uncommon to engage in complex regimens involving cleansers, serums, nutrients, as well as products to conceal imperfections. Of course, applying something topically does not address overall health—you don’t apply, say, eyeliner or skin moisturizer and tell yourself that you are now healthier, do you? Of course not. Products applied topically have limited benefits on the skin, mostly on the epidermis but not underlying dermis, no benefits for the rest of the body. And, of course, those expensive skin products you apply are washed off every night when you wash your face. You are not healthier, your skin is not healthier, as it is all superficial and temporary.

What goes on in the GI microbiome has a major influence over skin health. It’s been known for years that GI conditions such as irritable bowel syndrome, Crohn’s disease, and ulcerative colitis are often accompanied by skin conditions, for example. Let’s view skin as the outward reflection of overall health that reveals, for instance, hormonal status, inflammation, hydration, capacity for production of sebum and collagen, and other factors that are all under the influence of your GI microbiome.

As our understanding of the GI microbiome grows, it is becoming clear that the trillions of microbes dwelling in the 30-feet of GI tract can communicate with other parts of the body. What about the skin—is there a way for GI microbes to influence skin or the microbes residing on the skin? Yes: the gut-skin axis.

There are a number of ways in which the GI microbiome can “communicate” with the skin, i.e., the “gut-skin axis.” These include:

  • Production of microbial metabolites—The fatty acid, butyrate or butyric acid, is an example. Consume a food containing the prebiotic fiber inulin from onions, garlic, shallots, and other root vegetables, and GI microbiome species such as Faecalibacterium prausnitzii, Ruminococcus, and Clostridia species produce butyric acid that nourishes intestinal cells and, upon absorption, yields effects such as deeper sleep, reduced insulin resistance, and reduced blood pressure. Butyric acid (shown as SCFA or short-chain fatty acids in the above illustration) also reaches the skin where it helps generate an acidic pH that discourages growth of unhealthy microbes such as Staphylococcus aureus, often found at high levels in conditions such as eczema. Butyrate also reduces inflammation in the skin. The lack of skin butyrate may especially be important in the 20% of children who experience atopic dermatitis. Obtaining plenty of prebiotic fibers in your daily diet is therefore an effective strategy for maintaining healthy skin.
  • Endotoxemia—Recall that fecal microbes shed some of their debris into the intestine that then can, in turn, enter the bloodstream. This is how small intestinal bacterial overgrowth, SIBO, with trillions of microbes inhabiting the entire 30-feet of upper and lower intestines, “exports” effects far and wide to other parts of the body such as liver, heart, thyroid, brain, and skin. Because one of the most dangerous microbial breakdown products is called “endotoxin,” when it reaches the bloodstream it’s called “endotoxemia.” Endotoxemia can be prominently displayed on the skin as a variety of skin rashes, dryness, and premature wrinkles. This phenomenon is also  major factor in autoimmune skin conditions such as rosacea and psoriasis.
  • Gut-brain-skin axis—Restoring the microbe lost by most people due to its susceptibility to common antibiotics, Lactobacillus reuteri, allows it to take up residence in the entire length of GI tract where (if we extrapolate from the animal model evidence) it sends a signal via the vagus nerve to the brain to release the hormone oxytocin. Animal studies and limited human evidence (including our own human clinical study) suggest an increase in dermal collagen and an increase in sebum production that yields moisture.

Bottom line: Be sure to include plenty of prebiotic fibers in your daily diet routine, foods such as garlic, asparagus, leeks, dandelion greens; legumes such as white or black beans, chickpeas, hummus; nuts; and, for convenience, commercial prebiotic fiber powders. Look for evidence of SIBO and, if you believe you have it or test positive for breath hydrogen gas by the AIRE device, consider making my SIBO Yogurt that, so far, has been unexpectedly successful in normalizing H2 levels and correcting residual health issues. And get L. reuteri ATCC 6475, preferably as our L. reuteri yogurt with microbial counts of around 250-300 billion CFUs per 1/2-cup serving.