What is the gut-skin axis?
It is the idea that the state of the gut's bacteria and fungi directly affects the skin. The gases and metabolites made by overgrown gut microbes — or gut inflammation itself — can reach the skin barrier and immune system, leading to chronic skin conditions such as folliculitis, seborrheic dermatitis, rosacea, and atopic dermatitis.
Which skin conditions are linked?
Folliculitis (often mistaken for adult acne), seborrheic dermatitis, rosacea (facial flushing), and atopic dermatitis are the main ones. In atopic dermatitis, Staphylococcus aureus is detected at a far higher rate than in non-patients (~70% vs ~10%), and seborrheic dermatitis is strongly tied to overgrowth of the fungus Malassezia.
Why a "gut problem," not a "skin problem"?
When skincare and topical treatment only bring cycles of improvement and relapse, the cause may lie in the gut rather than on the skin surface. As long as bacterial and fungal overgrowth continues in the gut, treating only the skin suppresses the result — without addressing the cause, the same pattern keeps returning.
How does it work?
One known pathway: when the fungus Malassezia overgrows, the skin surface becomes alkaline, and this alkaline environment favors the growth of Staphylococcus aureus. As staph increases, water loss and further alkalinization compound each other, driving a vicious cycle in which skin immunity collapses.
Malassezia overgrows
The skin surface begins to alkalinize.
An environment for staph forms
The alkaline surface favors S. aureus.
Water loss + further alkalinization
The cycle accelerates.
Skin immunity collapses → chronic dermatitis
Presents as folliculitis, seborrheic dermatitis, atopy.
There are observations that the sulfur gases made by gut bacteria (H₂S, methyl mercaptan) affect systemic inflammation and mitochondrial function.
How is it assessed?
A breath test can check for small intestinal bacterial overgrowth (SIBO), and antigen-specific antibody testing can check for fungal hypersensitivity to Malassezia or Candida. Whether skin symptoms coincide with gut symptoms (bloating, gas, frequent changes in bowel habits) is also an important clue.
How is it managed?
The usual approach combines a diet that reduces bacterial and fungal overgrowth (low-substrate, refined-carbohydrate-centered), antibiotic and antifungal treatment when needed, and skin-surface care — together. Skincare alone can temporarily mask surface symptoms, but if the cause remains, relapse is likely.
Specific treatment must be decided through medical care.
Watch the skin and miss the gut, and the same relapse repeats.
8 years in clinic
Time spent working with skin–gut connected cases at a clinic in Gangnam, Seoul.
Atopy 70% vs 10%
The gap in S. aureus detection — not a lack of bacterial diversity, but the overgrowth of a single species.
Cover bacteria + fungi
Combining antibiotic and antifungal treatment with dietary change.
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The English-language writing on the gut–skin axis, SIBO, sulfur-reducing bacteria, and more lives on Substack.
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