Hair Loss

The Surprising Gut Connection Behind Some Hair Loss

The evidence here is moderate to early, built on real case reports and a specific causal mouse study rather than large human trials.

Hair loss has several distinct causes, including androgenetic alopecia, the most common pattern-based hair thinning, and alopecia areata, an autoimmune condition where the immune system attacks hair follicles directly.

Gut bacteria appear to play a genuine, if still developing, role in at least one of these.

Hair regrew unexpectedly after treatment for a gut infection

Two separate case reports describe patients with alopecia universalis, a severe form of alopecia areata causing complete hair loss, who received a faecal microbiota transplant (FMT), a procedure that transfers stool from a healthy donor to reintroduce gut bacteria, to treat an unrelated, recurring gut infection.

In both cases, the patients unexpectedly regrew hair in the months following the transplant, despite it never having been intended as a hair loss treatment.

Case reports like this can't prove cause and effect on their own, but they're a striking, real-world signal that gut bacteria may influence this specific autoimmune condition.

Source: Hair regrowth following fecal microbiota transplantation in an elderly patient with alopecia areata: A case report and review of the literature

A mouse study found a specific, causal mechanism behind this

Researchers found that disrupting mouse gut bacteria with the antibiotic vancomycin led one bacterium, Lactobacillus murinus, to overgrow and dominate the gut.

When these mice were also fed a diet low in biotin, a B vitamin important for healthy hair growth, they went on to develop hair loss.

This is a genuinely specific, testable mechanism: one bacterium overgrowing, combined with a lack of a specific nutrient it depends on, driving a measurable physical outcome. It gives real substance to the case reports above, rather than leaving them as an unexplained coincidence.

Source: Gut microbiome, metabolome and alopecia areata

Genetic evidence points to specific bacteria in pattern hair loss too

Separately from alopecia areata, researchers used genetic data to look for causal links between gut bacteria and androgenetic alopecia, the more common pattern-based hair loss affecting up to 80% of men and half of women by age 70.

Certain bacteria, including one from the family Acidaminococcaceae, were linked to a lower genetic risk of this type of hair loss, while others, including Roseburia, were linked to a higher risk.

This is still an early, developing area of research, using genetic prediction rather than direct experiments, but it points to gut bacteria mattering in the far more common, hormone-driven form of hair loss too, not just the autoimmune one.

Source: Causal relationship between gut microbiota and androgenetic alopecia: A Mendelian randomization study

What this means for you

Sudden, patchy, or rapidly progressing hair loss needs a doctor's assessment, since some causes are treatable and diagnosis affects which approach actually helps. In addition, the research above shows gut bacteria are linked to hair loss through more than one route, from a specific bacterium-and-nutrient mechanism in mice to genetic risk markers in the more common pattern-based form. A varied, plant-rich diet supports the same gut bacteria this research increasingly ties to healthier hair growth. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.