Primary scarring alopecias (PSAs) such as lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA) cause permanent hair loss, yet their exact causes remain unclear. Recent studies suggest that the scalp microbiome — the community of bacteria and other microorganisms living on our scalp — may play a role in triggering and driving these conditions. 

 

The scalp is a unique, lipid-rich environment that is home to diverse microbial communities, supported by hair follicles. In healthy scalps, studies using swabs consistently show that two bacteria — Cutibacterium acnes and Staphylococcus epidermidis — make up about 90% of all bacterial DNA sequences detected.1,2 These microbes are thought to help maintain balance (homeostasis) and protect against inflammation. 

 

Newer studies using biopsies and deep sequencing show that this balance can be disrupted (dysbiosis) in PSAs. Constantinou et al. found that Staphylococcus species dominated affected follicles, while Lawsonella species were more common in healthy scalps. This was linked to a higher Firmicutes-to-Actinobacteria ratio and increased production of beta-defensins (HβD1, HβD2), molecules involved in inflammation.3 In folliculitis decalvans, staphylococci (including MRSA and S. lugdunensis) are often isolated and are thought to sustain chronic inflammation.1 Pinto et al. found more Cyanobacteria and Euryarchaeota and less Firmicutes in LPP. Lower Microbacteriaceae levels were linked to higher IL-23 expression, suggesting that microbial imbalance may trigger immune responses that damage the follicle.4

 

Although different studies report different microbial changes, there is consistent evidence that the scalp microbiome is altered in scarring alopecias and that this may contribute to inflammation, follicle damage, and hair loss. Understanding these microbial shifts could help develop new diagnostic tools and inspire innovative therapies that target the microbiome to restore balance and reduce inflammation.

 

By Valentina Ross Massanes, MS – Pontificia Universidad Católica de Chile
Reviewed by Jorge Larrondo, MD, MSc. Clínica Alemana de Santiago

 

References

  1. Shah RR, Larrondo J, Dawson T, Mcmichael A. Scalp microbiome: a guide to better understanding scalp diseases and treatments. Arch Dermatol Res. 2024;316(8):495. Published 2024 Jul 29. doi:10.1007/s00403-024-03235-2
  2. Polak-Witka K, Rudnicka L, Blume-Peytavi U, Vogt A. The role of the microbiome in scalp hair follicle biology and disease. Exp Dermatol 2020;29:286–94..
  3. Constantinou A, Polak-Witka K, Tomazou M, Oulas A, Kanti V, Schwarzer R, et al. Dysbiosis and enhanced beta-defensin production in hair follicles of patients with lichen planopilaris and frontal fibrosing alopecia. Biomedicines 2021;9:266. 
  4. Pinto D, Calabrese FM, De Angelis M, Celano G, Giuliani G, Rinaldi F. Lichen Planopilaris: The first biopsy layer microbiota inspection. PLoS One 2022;17:e0269933. 

Read On