The haircare virtues of probiotics.

In haircare applications, probiotics are commonly found in shampoos or masks designed to soothe the scalp. These microorganisms can indeed work to reduce irritation and feelings of discomfort thanks to their anti-inflammatory and calming properties. Among the most used bacteria, we find the strain Lactobacillus reuteri, capable of downregulating the intracellular level of interleukin-8, a pro-inflammatory cytokine involved in the pathogenesis of psoriasis.

Probiotics derived from Bifidobacterium and Streptococcus have also demonstrated intriguing anti-inflammatory properties. These microorganisms function by stimulating the release of interleukin-10, an anti-inflammatory cytokine. Involved in the immune response, it inhibits the production of interleukins 2 and 3 and TNF-α, mediators of inflammation. Due to their various mechanisms of action, probiotics are interesting anti-inflammatory agents for soothing the scalp.

The overproduction of free radicals in the scalp, that is, oxidative stress, is harmful to hair follicles. Indeed, these reactive species can weaken these organs which can disrupt the hair cycle, promote hair loss and lead to split ends. Furthermore, free radicals affect melanogenesis by destabilising this process. The result: an acceleration of the natural whitening of hair fibres and a faster appearance of grey hair.

Probiotics can potentially offer protection to the scalp due to their antioxidant properties. This is particularly the case for so-called lactic bacteria, Gram-positive bacteria that produce lactic acid as the main product of their metabolism. When applied topically, these probiotics help to reduce the concentration of free radicals in cells. Furthermore, a recent study conducted in vitro has shown that the combination of β-nicotinamide mononucleotide and Lactobacillus fermentum can increase the levels of superoxide dismutase (SOD) and catalase, antioxidant enzymes. However, it should be noted that a murine model was used in these studies. It would be interesting to see if the results obtained can be replicated in clinical trials.

It is also attributed to certain probiotics the ability to accelerate hair growth. Among the most acclaimed strains, we find Bacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus and Lactobacillus rhamnosus. However, there are currently not enough scientific evidence to assert that the topical application of microorganisms has a real effect on the hair cycle. Most studies on this subject describe how to formulate a densifying shampoo based on probiotics, but these are not clinical trials attesting to their effectiveness.

In regards to the oral intake of probiotics, there is more evidence of its effectiveness on hair growth. A recent study conducted with 26 individuals experiencing significant hair loss demonstrated the benefits of twice-daily supplementation with Bifidobacterium lactis, Lactobacillus acidophilus, Lactobacillus rhamnosus and Lactobacillus paracasei. After 12 weeks, a significant improvement in hair density was observed in 25 individuals. Furthermore, 18 participants noted a decrease in their hair loss, but this measure is subjective. This study is thus encouraging regarding the potential effects of probiotics to promote hair growth. However, given that it only involved 26 individuals, more research is still needed.

• YU J. & al. Application and mechanism of probiotics in skincare: A review. Journal of Cosmetic Dermatology (2022).

• WANG J. & al. Impact of an oral probiotic formula on scalp and facial skin health, glucose, and lipid metabolism. Functional Foods in Health and Disease (2022).

• XU Z. & al. Applications of Probiotic Components in Cosmetics. Molecules (2023).