Psychobiotics: New era of microbiome science sheds light on topical probiotics for scalp health and mental well-being

21 Sep 2023 --- Microbiome supplementation initially targeted the gut microbiota but has since been extended to the skin. A new category explored in a Givaudan-led study, “psychobiotics,” is expanding the use of topical compounds with a positive action on microbiota, performing dermatological functions on the scalp while benefiting the host’s mental health.

In a new study, patchouli (Pogostemon cablin) leaf extract was proven to alleviate scalp dryness and was clinically evaluated on volunteers with dry and flaky scalps. In addition to looking at the physiological benefits of the leaf extract, its effects on stimulating emotions were assessed through three neuroscientific methods.

This study notably found that people with dry scalp have a different skin microbiota than people with oilier skin. It also pinpoints that the microbiota of people with dry scalp has more different types of organisms and less Cutibacterium bacteria. 

“Through this study, we proved that the skin microbiota of dry scalp was imbalanced, with increased alpha diversity [measure of the richness and evenness of a microbial community] and decreased Cutibacterium relative abundance compared to oilier skin,” comment the study authors.

“After applying our ingredient for one month, microbiota was rebalanced with a decrease in alpha diversity and increase in Cutibacterium relative abundance compared to the initial profile. Microbiota rebalancing led to an increase in scalp sebum and decrease in dry flakes compared to the start of the study.”

The researchers conclude that this “global” rebalancing improved the emotional state of people with scalp dryness who also expressed more positive emotions after treatment.

The research paper, published in the journal MDPI, consisted of a metagenomics study and sebum production analysis, coupled with flakes scoring. 

New microbiome supplements
Microbiome supplement products have existed for several decades and were initially designed to target the gut microbiota.

Now, three primary categories of microbiome supplementation have been created. The first is prebiotics, which are food components that positively affect the gut microbiota (e.g., lactulose, fructo-oligosaccharides and inulin).

The second category is postbiotics, which are substances resulting from microbiota metabolism and that have a beneficial effect on the microbiota itself as well as the host. The third category is probiotics, which are living microorganisms ingested for health benefits.

These definitions, which initially described ingested products for microbiome supplementation, were recently expanded to topically applied products having a beneficial effect on the skin microbiota.

Delving into functions of psychobiotics
A newly formed category of products dedicated to the microbiome are psychobiotics. They are defined by the study authors as beneficial bacteria or compounds that have a positive action on these bacteria, providing benefits to the host’s mental health. 

“Indeed, the communication between the gut and the brain has been studied in depth. Three major communication pathways have been identified: the hypothalamic-pituitary-adrenal axis, the immune response and neurotransmitters. These are three pathways that also interestingly link the skin microbiota to the brain,” they explain.

The research, conducted over a 28-day period, concluded that the application of the patchouli extract has a transformative impact on participants’ emotions.Scientists have discovered certain types of chemicals called short-chain fatty acids (SCFAs) that are made by the tiny living organisms in the gut and on the skin. These chemicals seem to play a role in how the body communicates with these microorganisms.

SCFAs are simple organic acids with a small number of carbon atoms, and the most common ones are acetate, propionate and butyrate. In the gut, SCFAs help control functions like digestion, the strength of gut lining, the immune system and even certain brain processes related to emotions.

Some studies suggest that when the body is given specific kinds of carbohydrates (oligosaccharides), it can help these microorganisms make more SCFAs. The researchers note that the patchouli extract used in the study is rich in oligosaccharides, which feed beneficial types of bacteria on the scalp.

The researchers suggest it is possible that the SCFAs produced by the microorganisms on the skin, like Cutibacterium acnes and Staphylococcus epidermidis, could have benefits like helping with dry scalp by balancing the production of skin oils. This further opens up possibilities for new skin care products.

Microscopic factories 
The research, conducted over a 28-day period, concluded that the application of the patchouli extract has a transformative impact on participants’ emotions. It was hypothesized that this mood enhancement could be attributed to two key factors.

First, the extract’s biological efficacy was seen in various aspects, from influencing gene expression to reducing the migration of keratinocytes (skin cells), decreasing skin thickness, and restoring the skin’s natural protective functions, including sebum production. 

This holistic approach led to a rebalancing of scalp sebum production and a reduction in the production of those troubling white flakes, making volunteers feel better just by not having to deal with this unsightly issue. 

The second hypothesis revolves around the patchouli extract’s ability to harmonize the composition of the scalp’s microorganisms and regulate sebum production, bringing it closer to the levels found in a “normal” scalp. By reactivating sebum production, it creates an environment conducive to the growth of Cutibacterium acnes, the bacterium known to produce SCFAs that have been linked to positive effects on mood when ingested. 

The results strongly aligned with psycho-dermatology studies, indicating that people grappling with skin issues, such as dry or sensitive skin, are more susceptible to feelings of depression, anxiety and general emotional distress.

Further research is underway to delve deeper into these findings.

By Benjamin Ferrer