Gut Skin Axis

You’ve probably heard of the critical importance of gut health by now. And possibly of the gut-brain axis …. but have heard of the gut-skin axis? Are the gut and the skin connected? This blog will answer those questions so read on for more info!

In this blog, you will learn:

• What is the gut-skin axis?
• Are the two really connected?
• What does the gut-skin axis mean for your skin health?

What is the Gut-Skin Axis?

The Gut

The gut microbiome is the foundation of health. The gut houses trillions of microbes (bacteria, fungi and viruses). Some of these microbes are beneficial and support gut health and some are pathogenic and can cause health problems. 

The variety and composition of the trillions of gut microbes varies significantly between different people. The composition of these microbes in the gut strongly influences one’s health. 

The Skin

As the body’s largest organ, the skin is a defense barrier against environmental threats, injuries and microbes. The skin has a microbiome of its own, which is important for skin health. More than 1,000 different bacteria and microbes live on the skin (Mahmud MR, 2022).  

The gut-skin axis is the two-way relationship between the gut microbiome and the skin. It influences skin health. Gut and skin microbiota are important in skin health and skin diseases (Chai J, 2024).

Mechanisms of Gut-Skin Axis  

The Immune System 

Poor gut health negatively affects the immune system. This is because the gut is home to 80% of the immune system in the form of the various types of immune cells. The gut helps modulate immune responses and regulates inflammation.

The immune system protects the body from pathogens and other foreign invading substances. The gut microbiome interacts with the immune system and with the skin to manage inflammation. 

The gut lining and the skin have direct contact with the external environment and are both covered by epithelial cells (ECs). Epithelial cells are a type of skin cell. They act as a first line of defense between the body and the outside world, preventing microorganisms from entering the body (De Pessemier B, 2021). ECs are part of the immune system, protecting the body from harmful substances. 

Microbial Metabolites

The gut microbiome produces microbial metabolites. These are small molecules made by microbes in the gut. The gut microbiome produces at least 30 different microbial metabolites (De Pessemier B, 2021). Examples are short chain fatty acids (SCFAs), bile acids, cortisol, vitamins like vitamin K2 or B vitamins, neurotransmitters such as GABA, serotonin, dopamine, and tryptophan. Microbial metabolites are produced by the gut microbiome and released into the bloodstream. They affect various organs, including the skin (De Pessemier B, 2021).

Microbial metabolites can influence immune cell function, cytokine release and inflammation. They can travel through the bloodstream and affect the skin barrier. 

Microbial metabolites can be beneficial. They can reduce inflammation, improve immune cell balance in the gut and indirectly benefit skin health. 

• GABA, acetylcholine, dopamine and serotonin are among the neurotransmitters produced by gut microbes. Neurotransmitters can have positive or negative effects on the skin (Mahmud MR, 2022). 
• GABA increases the expression of collagen and maintains skin elasticity (Mahmud MR, 2022). 
• Dopamine can inhibit hair growth (Mahmud MR, 2022).

Gut Dysbiosis 

Dysbiosis is the imbalance of good and bad bacteria/microbes in the gut. In dysbiosis, bad pathological bacteria outweigh the good beneficial bacteria. Certain species of pathogenic bacteria can overgrow when there are not enough healthy bacteria. Healthy bacteria are needed in the right number to keep the pathogenic bacteria under control and to maintain a healthy gut microbiome balance. Dysbiosis disturbs this balance, dysregulates the immune system, increases inflammation and affects skin health (Mahmud MR, 2022).  

Leaky Gut

Dysbiosis can compromise the gut lining or gut barrier integrity. Dysbiosis, and other factors (gluten, stress, alcohol to name a few), can damage the gut lining. These factors loosen the tight junctions of the gut, effectively causing tiny little holes in the gut lining. This leads to microbes and bacteria being able to pass through the intestinal barrier. These gut microbes, toxic products, neurotransmitters and altered immune cells pass into the bloodstream and can then circulate throughout the entire body. These substances are toxic in circulation and can cause the immune system to react and overreact. This impairs immune cell behavior, leads to an immune overactivation and can contribute to skin issues, allergies and possibly autoimmune conditions (Mahmud MR, 2022).

This type of damage to the gut barrier integrity is commonly called intestinal permeability or leaky gut. Leaky gut can have a significant impact on skin health. 

Gut barrier integrity is important for skin health. A strong gut barrier prevents the gut bacteria /microbiota from exiting the gut and helps prevent gut inflammation. If pathogens circulate and immune function becomes impaired, dysbiosis of the skin can happen. Dysbiotic skin microbes can inflame the skin and contribute to the onset of skin disorders (Mahmud MR, 2022).

Gut dysbiosis is often linked to inflammatory diseases. Inflammatory gut issues are often associated with skin problems. For example, 7–11% of patients with IBD also have psoriasis (De Pessemier B, 2021). 

Skin Disorders

Gut health can have systemic effects throughout the body, including on skin health. Skin diseases can be significantly linked to the gut microbiome, as well as the skin microbiome (De Pessemier B, 2021). Other factors involved in developing skin diseases include genetic tendencies, lifestyle and immune system health (which is dependent upon gut health). 

Dysbiosis and the strength of the gut barrier is very important. If compromised, leaky gut develops. This can worsen gut microbiome health and cause skin conditions. Specific metabolic byproducts of gut microbes can directly influence skin disease processes. 

Dysbiosis in the gut contributes to common skin disorders. Acne, atopic dermatitis or eczema, psoriasis, and rosacea are all specifically linked to gut dysbiosis (Mahmud MR, 2022). The gut microbiome can also significantly contribute to allergies and asthma (Mahmud MR, 2022).

Atopic dermatitis, or eczema, is a condition of dry, itchy, inflamed skin. The gut microbiome, skin barrier and immune system are all involved. Unhealthy immune responses linked to an unhealthy gut-skin axis can contribute to skin inflammation, dryness and allergic reactions (Mahmud MR, 2022). 

In psoriasis, gut dysbiosis and leaky gut affect immune cell function and cytokine production, leading to skin inflammation and psoriasis skin patches (Mahmud MR, 2022). 

What Influences the Gut-Skin Axis?

The composition and variety of gut microbiota affects the gut-skin axis, the skin microbiome and skin health. Diet, prebiotics, probiotics, antibiotics and other lifestyle factors influence the gut microbiome. Skin inflammation can result from even small changes in the gut microbiome. These factors can lead to diseases like acne, dermatitis, psoriasis, rosacea or other skin conditions.

Some examples of how different microbial species affect the skin are (Mahmud MR, 2022):

• The gut bacteria Faecalibacterium prausnitzii, Akkermansia muciniphila and Ruminoccocus protect against psoriasis by preventing pathogenic flora from colonizing the skin.
• The common bacterial infection Helicobacter pylori can contribute to rosacea. This happens via increased production of cytokines and reactive oxygen species. These can cause gut inflammation, skin inflammation and negative changes in the immune system (Mahmud MR, 2022).
• Some pathogenic bacteria cause dysregulation and inflammation of the gut lining, leading to leaky gut. Some gut organisms can cause immune system dysregulation and skin inflammation.
• Some gut metabolites can decrease inflammation and improve the integrity of the gut lining.
• Good bacteria like Lactobacillus casei reduce skin inflammation by reducing inflammatory cells. Lactobacillus paracasei decreases acne lesions and inflammation and helps heal the gut barrier.

How to Optimize the Gut-Skin Axis for Skin Health

Gut and skin health can be improved through factors within our control. Diet is a key element we can use to optimize and improve gut and skin health. Supplements, medications and other lifestyle factors also count. 

Which Diet Benefits the Gut-Skin Axis?

It is important to follow a diet that supports gut health. We have written a blog here on the diet plan that can heal leaky gut. This is a good approach to general gut and gut-skin axis support. 

In a nutshell, eat:

• Whole foods – vegetables, some fruit, good fats, clean protein, anything natural and unprocessed.
• Polyphenols and antioxidants from any vegetables & fruit, the darker the color the more antioxidants. Aim for a minimum of 30 plants per week.
• High fiber whole foods – fruits, vegetables, legumes, chia/ flax seeds – promote good gut health.
• Clean proteins – Organic grass-fed meats, organic chicken, eggs, fish, plant-based proteins (pea, legumes, whey or protein powders) help repair and regenerate skin and support a healthy skin barrier. 
• Eat fermented foods which contain probiotics (yogurt, kefir, sauerkraut, kombucha, kimchi). They add good bacteria to the gut, support a diverse and healthy gut microbiome and positively impact skin health. 
• Prebiotic foods from cooked and cooled white rice or white potatoes, oats, apple, raw onion, garlic, asparagus, unripe banana. Prebiotic foods feed the good gut bacteria. 
• Good fats from olive oil, avocadoes, nuts, seeds, omega 3 from oily fish (SMASH: sardines, mackerel, anchovies, (wild) salmon, herring)

Specific diets such as low calorie/ caloric restriction and low fat (reducing the bad inflammatory fats from processed foods/vegetable oils) help improve intestinal permeability and skin issues such as acne, atopic dermatitis, psoriasis, wound healing, skin cancer and even skin aging (De Pessemier B, 2021). 

Dietary Fiber

Fiber is healthy for the gut microbiome. High fiber foods increase Bifidobacteria and the Lactobacillus/ Enterococcus species of bacteria. These are converted into SCFAs through fermentation by the gut microbiome. SCFAs strengthen the gut function and integrity, reduce inflammation, prevent inflammatory disorders (allergies, arthritis, colitis) and inhibit harmful metabolic by-products. SCFAs also strengthen immune defense mechanisms of the skin. They prevent bad bacteria from growing on the skin, decrease inflammation and support the skin microbiome and immune system.