Probiotic Hair Care - Where is it, When You Need it? #SV Reviewing the Research that Could Bring Your Hair Back

The idea of probiotic shampoos has been thrown around for quite some time, now. Gonna get rid of the text-containing thumbs, btw.
I've recently got a request by a SuppVersity reader suggesting I write something about #hairloss... well, I thought: "I've addressed all there is in the two older articles on hair loss," and a cursory search of the latest literature seemed to confirm just that. It (or the absence of corresponding research) did yet also trigger my interest in the role of the microbiome in hair loss, hair maintenance, and hair regrowth... and I am not referring to expensive (useless) probiotics you'd swallow and hope for magic on your scalp. What I wanted to know was: Do we know anything about the scalp microbiome?
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And *bang* 107 results on related directly or indirectly to the "scalp microbiome". Many of them are related to non-hair-loss conditions, though. Still, the mere existence of a hitherto completely ignored (by the hair product industry) bacterial ecosystem on your head is mindboggling.

What do we know about the scalp microbiome, in general?

Certain characteristics, like high Propionibacterium levels, and lower bacterial diversity have been linked to sensitive scalp skin (Ma 2019). An even more recent review presents evidence in favor of a continuous exchange between the microbes on your skin with the cutaneous immune system in healthy skin, where hair follicles (HFs) provide unique anatomical niches, stating: 
Figure 1: Illustration of the proposed mechanism.
"Especially, scalp HFs form large tubular invaginations, which extend deeply into the skin and harbour a variety of microorganisms. The distinct immunology of HFs with enhanced immune cell trafficking in superficial compartments in juxtaposition to immune‐privileged sites crucial for hair follicle cycling and regeneration makes this organ a highly susceptible structure. Depending on composition and penetration depth, microbiota may cause typical infections, but may also contribute to pro‐inflammatory environment in chronic inflammatory scalp diseases." (Polak‐Witka 2020)
Pro-inflammatory? Now, your alarm bells should be ringing. Inflammation is, after all, at the root of all modern chronic diseases. Your dome could thus be an "inflammatory disease" and the latter could be triggered by effects of your scalp microbiome on hair cycle regulation and immune cell maturation. 

Is there a role in androgen-induced (or ascribed) hair loss?

The issue of having the wrong scalp microbiome (or none at all?) obviously matters for alleged androgen-induced hair loss, too. Either by making the sufferers more susceptible to DHT's effects on their hairline or because the supposedly androgen-related receding hairline is in fact 'eaten away' by bacteria - more or less irrespective of DHT. 
Figure 2: Left - Control. The arrow shows a biofilm in the cuticle of the hair bulb. In green, along the hair shaft there are two fragments of epithelial root sheaths. Right - Patient suffering from folliculitis decalvans and hair loss. Hair plucked in normal‐appearing skin. Biofilms (arrows) are situated in the suprabulbar area, along the cuticle of the hair shaft, growing in the thickness of the inner root sheath (Matard 2013). The same mechanism is supposed to play an important role in other diagnoses that involve hair loss ... maybe your's too?
In fact, this form of hair loss experts call "androgenetic alopecia" (#AGA) features shortening of the anagen phase and a slowly progressing miniaturization of the hair follicle over time, an impairment that could be related or even triggered by a messed up microbial colony on your scalp... and voilà 
"Infiltration of mononuclear cells and lymphocytes is detected in about 50% of skin samples [of patients with diagnosed androgenetic alopecia]. This micro‐inflammation takes place in the upper third of the [hair follice] HF, where a great number of microorganisms are harboured. Moreover, porphyrins stimulating the production of complement and produced by Cutibacterium spp. were identified in the pilosebaceous duct of 58% of patients with AGA compared to 12% of the control group." (Polak‐Witka 2020)
In view of these scientific facts, it cannot be surprising that researchers report significant improvements of #AGA after application of antimicrobial agents - the same agents that have a much broader scientific backing for seborrheic scalp dermatitis (Kibar 2014) or acne vulgaris.
Dandruff sufferers are more likely to suffer from a lack of microbial diversity and an increased population of certain scalp bacteria (Saxana 2018).

Also on the list of potentially microbial scalp issues are:
Everything from excessive dandruff (see figure on the left), over Folliculitis decalvans, a type of primary cicatricial alopecia with unclear pathophysiology, and Psoriasis, a chronic T cell‐mediated disorder, probably developing as a result of a combination of genetic background and external triggering factors, such as drugs, microorganisms and stress, to patches of Alopecia areata a type of non‐scarring alopecia considered to be of autoimmune origin. And theoretical they could be involved mechanistically and/or as a symptom of all sorts of reasons of weight loss 🤔.
No wonder scientists have long been excited that their research results and methodology related to the far-reaching effects of stool microbiome will soon be adapted to the skin. They propose a similar protective effect of the 'right' bacteria that prevent the "unwanted pathogens from colonizing" (Kibar 2014). This could correlate with intestinal issues but certainly doesn't have to, as it seems quite clear that the bacteria invade the follicle from the surface, and are not transported via the portal vein into the blood circulation and from there into your hair... that a healthy gut will help with skin health stands out of question, though.

'Topical probiotics' 🦠 to the rescue? 

Compared to oral probiotics and the microbiome of your digestive tracts, little research exists on interventions to improve the scalp microbiome. On the other hand, there's plenty of evidence of the usefulness of washing your hair with certain essential oil... and those, you know that, are notorious for having anti-microbial effects. The same goes for lauric and sapienic acids from coconut oil (the former), and fatty cheese and meats (the latter), respectively.

Other agents that even have scientific back-up for their ability to modulate scalp microbiome in hair loss scenarios are based on traditional medicine Lindera strychnifolia roots (#LsR) extract, for example, has been shown to be a natural solution for the modulation of the scalp microbiome in androgenetic alopecia (Filaire 2020). And the results of the recently published paper are promising as they "suggest that LsR extract may be a potential remedy for scalp microbiota re‐equilibrium."(Filaire 2020).
Hair Loss: Finasteride, Laser Light or Minoxidil - What Will Really Help Men & Women Regrow Lost Scalp Hair? This is one of the articles from the SV archives, the other one is on nutrients and supps vs. hair loss; and the latest article addresses the hair growth prowess of (synthetic) sandalore (check it out! in the SV archive).
No products on the mass market, yet, but just wait... I can almost guarantee that the big players will jump the probiotic train (as usual with underdosed products) as soon as a start-up started collecting money for their probiotic hair care on indiegogo.  (a small company already sells a product in Europe and North-Africa | #noRecommendation). That's how this industry is operating. 

In the meantime, it may be a good idea not to wash your hair every day or to stick to products with few ingredients of which you can be sure that they don't trigger an imbalance of your scalp's microbiome. Using topical antibiotics, though, is not recommended before we know how to replace the by then eradicated pathogenic microbiome with a healthier one (just as in the gut, the antibiotics my actually promote the post-treatment growth of harmful bacteria) | Comment.
  • Kibar, Melike, Şebnem Aktan, and Muza severity." Annals of dermatology 26.4 (2014): 478-484.
  • Ma, Li, et al. "Sensitive scalp is associated with excessive sebum and perturbed microbiome." Journal of cosmetic dermatology 18.3 (2019): 922-928.
  • Matard, B., et al. "First evidence of bacterial biofilms in the anaerobe part of scalp hair follicles: a pilot comparative study in folliculitis decalvans." Journal of the European Academy of Dermatology and Venereology 27.7 (2013): 853-860.
  • Polak‐Witka, Katarzyna, et al. "The role of the microbiome in scalp hair follicle biology and disease." Experimental dermatology 29.3 (2020): 286-294.
  • Saxena, Rituja, et al. "Comparison of healthy and dandruff scalp microbiome reveals the role of commensals in scalp health." Frontiers in cellular and infection microbiology 8 (2018): 346.
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