The gut and skin are both complex immune and neuroendocrine (of, relating to, or being a hormonal substance that influences the activity of nerves) organs, and each has a community of microbes that governs the physiology of their local surroundings.
A 3-directional communication among the brain, skin, and gut, along with influences from the immune and endocrine systems, has been identified, although not fully understood. Pathology of the gastrointestinal tract and diet have been shown to influence skin health. Many skin conditions have been linked to gastrointestinal inflammation, including rosacea, psoriasis, and acne. Skin lesions can also occur in association with gastrointestinal conditions such as inflammatory bowel disease (IBD) and celiac disease.
The recognition that the gut and skin are connected is not new; traditional forms of medicine that have been around for thousands of years, such as Ayurvedic medicine and traditional Chinese medicine, have a gut-centric approach to health and disease. As research continues to expand in this area, the notion of a gut-skin axis has started to emerge in Western research.
Modes of Communication From the Gut to the Skin
The gut may communicate with the skin in several ways:
- Absorption of nutrients with a direct effect on the skin
- Absorption of nutrients that can stimulate hormonal changes that affect the skin
- Influence of gut microbiota on the immune system
- Modulation of the local microbiome that releases metabolites that may have distant effects on the skin
Absorption of nutrients with a direct effect on the skin
The absorption of nutrients and their direct effects on the skin has been a focus of several studies. For example, the intake of carotenoids has been correlated to yellowing of the skin, and beta-carotene supplementation has been studied in the prevention of sunburns. In addition, oral vitamin E can be delivered to the skin, especially through sebaceous (oil) glands.
Absorption of nutrients that stimulate a change in hormones
Absorbed nutrients frequently shift hormones in the body. Examples include the influence of carbohydrates and whey protein on insulin levels, which can have an impact on the skin. As an example, whey protein may be associated with increased insulin secretion and has been reported as a potential culprit in acne flares. Insulin-like growth factor 1 (IGF-1) activates the sebaceous glands to produce more inflammatory mediators and more sebum, which may trigger a worsening of acne. So, consuming more high-glycemic, refined carbohydrates may increase the concentration of IGF-1 and increase the risk of developing acne.
The influence of gut microbiota on the immune system
The gut microbiota interact with the immune system and appear to interact with and educate the regulatory T cells that can drive inflammation elsewhere in the body. Regulatory T cells seem to play an important role in autoimmune and inflammatory skin diseases although the role of the gut microbiome remains under study in these areas.
Modulation of the local microbiome and influence on the local immune system
The microbiota and the gut lining interact and release secondary metabolites that can have distant effects on the skin. Previous studies have suggested that changes in gut microbiota and the microbiota-derived inflammatory mediators may impact chronic inflammation and the risk for cardiovascular disease, obesity, kidney disease, and diabetes.There is growing evidence that gut-derived mediators may communicate with the skin as well.
Examples of mediators include lipopolysaccharide (LPS) and short chain fatty acids. It has been hypothesized that gut-derived LPS may play a role in acne inflammation, though definitive mechanistic studies are still lacking. Short-chain fatty acids have long been postulated to affect general inflammation in the body and modulate obesity, diabetes, and colon cancer risk.
Short-chain fatty acids may modulate inflammation, and patients with acne have lower blood levels of these fatty acids than healthy controls (Sivamani, unpublished data, 2018).
While these mechanisms may not serve as a comprehensive examination of the gut-skin axis, they bring to light the gut’s ability to communicate with the skin through multiple modalities.
Apart from possible mechanisms, there are several lines of evidence that suggest that gut dysbiosis is involved in skin disease.
Disease-Based Examples of Gut Dysbiosis in Skin Disease
Dysbiosis an imbalance of the intestinal microbiota. Small intestinal bacterial overgrowth and papulopustular rosacea.
Often mistaken for acne, papulopustular rosacea can occur with erythematotelangiectatic rosacea, and is characterized by erythema, papules, and pustules. Papulopustular rosacea is not only associated with a dysbiosis of the skin microbiome, but also with small intestinal bacterial overgrowth (SIBO), a dysbiosis of the intestinal tract.
Dysbiosis and psoriasis
One recent study comparing the gut microbial composition of patients with psoriasis to that of healthy patients found that psoriasis patients had an increased presence of Faecalibacterium and decreased Bacteroides compared to the healthy controls. A similar study found that, compared to healthy controls, psoriasis patients had an increased ratio of Faecalibacterium to Bacteroides in the intestinal microbiome and an increase in Streptococcus and decrease in both Propionibacterium and Actinobacteria on the skin’s surface.
The recognition that the gut and skin are connected is not new; traditional forms of medicine that have been around for thousands of years, such as Ayurvedic medicine and traditional Chinese medicine, have a gut-centric approach to health and disease.
High-glycemic diet and acne vulgaris
The Standard American Diet (SAD) is a high-glycemic diet rich in processed fast foods, refined carbohydrates, animal proteins, and omega-6 polyunsaturated fatty acids. Seventy-five percent of Americans consume a Standard American Diet. Studies have shown that consuming a Standard American Diet increases pro-inflammatory mediators. Leucine, an amino acid found in animal protein and dairy products, stimulates the oil glands and can create inflammation, causing breakouts.
The consumption of a SAD increases the secretion of androgen hormones such as testosterone, which activates mTORC1 to stimulate the sebaceous follicles to produce more sebum. Acne is recognized to be diet-driven disease. Areas where high-glycemic diets are not consumed, such as in isolated hunter-gatherer communities, have extremely low rates of acne.
Inflammatory bowel disease and various skin lesions
Crohn’s disease and ulcerative colitis are the 2 main categories of IBD. Their pathophysiology is not limited to the gastrointestinal tract; IBD is associated with extraintestinal manifestations in 6% to 47% of patients. In 25% of patients with IBD, the extraintestinal manifestations precede the diagnosis of Crohn’s or ulcerative colitis. Although the mechanism is not well-understood, information collected from a clinical trial suggested that blockade of tumor necrosis factor (TNF) may play a role in the pathogenesis of these skin conditions in IBD.
Celiac disease and dermatitis herpetiformis
Dermatitis herpetiformis is an extremely pruritic eruption seen on the buttocks and the extensor surfaces of the extremities. It affects approximately 17% of patients with celiac disease, though it may not be detected until up to 10 years after the celiac disease diagnosis. In most cases, dermatitis herpetiformis in patients with celiac disease indicates poor adherence to a gluten-free diet.
The Role of Probiotics
When oral probiotics are ingested, they can have effects on distant organ systems through the immune system. Through interactions with lymphoid tissue, probiotics may regulate the release of inflammatory cytokines that are often increased in various skin conditions. There is evidence supporting the use of probiotics for skin conditions. There are many species of probiotics, and there are specific types recommended for specific conditions.
While questions still remain, there is no doubt that further research into the gut microbiome and how it contributes more widely to general health is exciting. As our knowledge grows regarding how food, probiotics, and the gut microbiome modulate health, it is our hope that our dietary and lifestyle patterns will shift toward both healthier skin and a healthier metabolic state.
If you need help selecting a proper probiotic supplement, Skinplicity has many options available through their supplement prescribing platform FullScript.