Gut – Skin Axis: Eczema

Gut health is critical for skin health. We have recently written about the gut-skin axis, psoriasis, psoriasis treatment, and rosacea. Today we look at eczema, another skin condition related to the gut-skin axis. 

In this blog, you will learn:

• What is eczema? 
• How is eczema related to the gut and the gut-skin axis?
• What are the triggers for eczema?
• How can eczema be treated naturally?

What is Eczema?

Eczema is a non-contagious chronic inflammatory skin condition. It causes dry, itchy, scaly and inflamed patches or blisters. There are different types of eczema. Atopic dermatitis (AD) is the most common type and represents up to 80% of eczema cases. We will primarily address AD in this blog. Other eczema types may have different triggers and require tailored management strategies. 

Typically, symptoms first develop in childhood. AD is prevalent in 25% of children and 7–10% of adults (Wang Y, 2024). It is often the first indicator that someone has allergies, which can progress from eczema to allergic rhinitis (hay fever), allergic conjunctivitis (itchy red eyes related to hay fever) and asthma. 

Eczema & the Gut–Skin Axis

Gut bacteria diversity and composition is closely related to allergic diseases like asthma, food allergies and atopic dermatitis (Nekrasova AI, 2024). Dysbiosis in the gut or skin microbiome is the common issue that can lead to eczema. Dysbiosis is when the gut or skin microbiome is out of balance. It can be a case of too many bad bacteria, not enough good bacteria and/ or not enough diversity of bacterial species. The imbalance decreases bacterial diversity. Lower beneficial bacteria usually results in more pathogenic bacteria in the gut. Low bacterial diversity is associated with immune-mediated disorders because gut health, gut bacteria and immune cells all impact the immune system. 

Dysbiosis impairs gut function, lowers gut bacteria diversity and decreases SCFA (short chain fatty acids) production. Certain strains of good bacteria produce SCFAs. With more pathogenic bacteria and lower levels of good bacteria, less SCFAs are produced. This creates a cycle of inflammation and dysbiosis. Dysbiosis is damaging to the gut lining and to immune function. Dysbiosis can lead to leaky gut and abnormal immune function. People with AD likely have dysbiosis, leaky gut and low production of SCFAs. A leaky gut lets toxins and pathogens pass through the gut lining which systemically increases pro-inflammatory cytokines. People with AD have high levels of the antibody IgE and mast cells. With an allergy, the immune system overreacts to a harmless substance (an allergen) and produces IgE antibodies against it. These IgE antibodies and mast cells can damage the gut lining, cause an inflammatory response and trigger allergy symptoms.

Gut bacterial diversity and abundance is critical for good health. Healthy people have more diversity and abundance of bacterial species in the gut microbiome. They have more protective bacteria such as Prevotella, Lactobacillus, Streptococcus, Bifidobacterium and Faecalibacterium (Díez-Madueño K, 2024). 

People with eczema have lower diversity and more pathogenic bacteria (Díez-Madueño K, 2024). Certain bacterial species are more common in people with eczema. 

• Children with AD have lower diversity of gut microbes compared to healthy children. 
• People with eczema have less abundance of SCFA-producing bacteria. 
• People with eczema have higher levels of Clostridium difficile, Escherichia coli and Staphylococcus aureus in the gut microbiome (Díez-Madueño K, 2024). 
• Good bacteria like Bifidobacteria, Bacteroidetes and Bacteroides are lower in those with AD (Nekrasova AI, 2024). 

Lower Short Chain Fatty Acids or SCFAs

The primary SCFAs are acetate, propionate and butyrate. SCFAs a are produced by good gut bacteria. 

SCFAs reduce inflammation and regulate immune function. SCFAs decrease pathogenic bacteria species and break the dysbiosis-inflammation cycle (Díez-Madueño K, 2024).

Butyrate and other SCFAs reduce inflammation in the gut and other parts of the body. They influence immune cell activity and inhibit the production of pro-inflammatory cytokines. SCFAs support the growth of beneficial bacteria and a strong gut barrier function. In the case of dysbiosis, the fewer good bacteria produce fewer SCFAs. This can weaken and damage the gut lining and potentially worsen inflammatory skin diseases. 

Lower butyrate and propionate levels are associated with AD (Díez-Madueño K, 2024). Butyrate encourages immune cells to promote immunotolerance. In AD, dysbiosis and the lower SCFA production can cause an increased inflammatory response (Díez-Madueño K, 2024). 

Leaky Gut & Immune Activation

With dysbiosis, the gut lining may become permeable or leaky. A leaky gut lets toxins (like bad bacteria, lipopolysaccharides) leak into the bloodstream. The toxins leak out and then circulate throughout the body. This activates the immune system and, in the case of a leaky gut, happens repeatedly. The constant activation and eventually overactivation of the immune system creates inflammation, contributes to inflammatory conditions and possibly starts an autoimmune process. 

The inflammatory response triggered by an overactive immune system can be seen anywhere in the body. In the case of eczema, it is the skin that is affected. Gut inflammation caused by leaky gut can weaken the protective function of skin, which can increase inflammation and worsen eczema symptoms.

Autoimmune Process?

Neither eczema nor atopic dermatitis is considered an autoimmune disease, though it does involve the immune system. The immune system influences the inflammation and itching associated with eczema. But the immune system in this case does not target a specific body part/organ as it does in autoimmune conditions. In autoimmune diseases, the immune system mistakenly attacks the body’s own healthy tissues or cells. Instead, eczema involves a dysregulated gut-skin axis and an overactive and inflammatory immune response to various triggers. Eczema is not classified as an autoimmune disease.

The Skin Microbiome

The gut-skin axis, the skin microbiome and the gut microbiome influence the immune system and skin barrier. A weak skin barrier can affect skin health. In atopic dermatitis, there is an issue with the skin barrier, inflammation and dysbiosis of the skin and gut. A dysbiotic or imbalanced skin microbiome affects the immune system and stimulates inflammatory reactions which can present as AD (Mazur M, 2023).

In AD, the skin barrier is dysregulated, possibly because substances needed for epithelial (i.e. skin) health and integrity may be dysfunctional (Kolb & Ferrer-Bruker., 2023). As in the gut microbiome, the good bacteria of the skin protect the skin from pathogens and keep the immune system in balance. This avoids an excessive immune response and inflammation. Some good skin bacteria produce antimicrobial substances that fight pathogens to reduce the number of bad skin bacteria. A strong skin barrier limits inflammation (Mazur M, 2023). 

A dysbiotic and damaged skin barrier lets allergens and toxins penetrate the skin and allow pathogenic microorganisms to colonize the skin. This causes inflammation through an overactive immune response (with increased cytokines). Scratching the skin can also stimulate inflammatory cytokines (Kolb & Ferrer-Bruker., 2023). 

In eczema, there are less anti-microbial peptides in the skin. This allows colonization by the pathogenic bacteria Staphylococcus aureus. This is seen in over 90% of atopic dermatitis patients (Kolb & Ferrer-Bruker., 2023). Staphylococcus aureus is a type of bacteria commonly found on human skin. S. aureus may worsen inflammation and cause an excessive immune response. This weakens the skin barrier (Mazur M, 2023). It is not clear whether people transfer S. aureus bacteria with their hands by scratching, or whether immune system deficiencies allow for the colonization of S. aureus. Strains of S. aureus isolated from AD patients were found to secrete exotoxins which damage the skin barrier (Mazur M, 2023).