The follicular microbiome in hair-follicle-associated inflammatory diseases: a systematic review.
Agathe Franz, Andria Constantinou, Doris Wilborn et al.
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In 30 seconds
This systematic review qualitatively synthesized culture-independent studies of the bacterial hair-follicle microbiome in inflammatory hair-follicle-associated diseases. It included 55 studies involving 1811 patients from 19 countries. Despite substantial variation in sampling and laboratory methods, Cutibacterium and Staphylococcus were the genera most often reported as altered. Staphylococcus abundance was generally increased across diseases, while Cutibacterium findings varied by condition. Results were inconclusive for alopecia areata and rosacea. The review identifies recurring microbial patterns but concludes that their causal significance remains unclear.
Key findings
- The review included 55 studies involving 1811 patients from 19 countries.
- Staphylococcus showed increased relative abundance across diseases, particularly in scarring alopecias, seborrhoeic dermatitis/dandruff, and acne.
- Reduced Cutibacterium abundance was reported in seborrhoeic dermatitis/dandruff, while Cutibacterium acnes appeared more prevalent in androgenetic alopecia.
- Findings were inconclusive for alopecia areata and rosacea; hidradenitis suppurativa findings suggested enrichment of anaerobic opportunists, including Porphyromonas and Prevotella.
Why it matters
The review brings together evidence that follicular microbial communities may differ across several inflammatory skin and hair disorders. These recurring patterns can help frame research into disease biology, but substantial methodological variation and uncertain causality mean they should not be interpreted as established mechanisms or treatment targets.
What to keep in mind
The included studies varied substantially in sampling, storage, DNA extraction, sequencing, and analysis, limiting confidence in comparisons across diseases.