Like to tan? Mind your skin microbiota!
Exposure to the sun’s rays may cause an imbalance in the microbial community living on the surface of the skin, with those who like to tan apparently most at risk
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About this article
Do you feel more beautiful, healthier, and attractive when tanned? Unfortunately, your skin microbiota does not agree... And neither does your health!
So concludes a study 1 on a group of 4 men and 17 women from Northern Europe who spent at least a week on vacation basking in the sun.
The day before their departure, the researchers took a skin sample from the most tanned part of the participants’ forearms in order to analyze the composition of their skin microbiota. They repeated this the day after the participants’ return (D1), 28 days later (D28), and then after 84 days (D84).
To determine their phototype and changes in their tans, the scientists also measured the color of the skin on their “posteriors” (low exposure to sun) and forearms, both before and after sun exposure.
To each their own sun exposure...
The results?
Firstly, it was possible to classify the volunteers into three groups:
- The “tanning enthusiasts”, who spent a lot of time in the sun during their vacations;
- The “already tanned”, who had tanned skin before departure and kept it that way;
- The “wary”, who were minimally tanned before leaving and managed to protect themselves from the sun.
The researchers went on to report that in all the volunteers, three major bacterial phyla – Actinobacteria, Proteobacteria, and Firmicutes – accounted for 95% of all microorganisms.
However, on D1, just after returning from vacation, the “tanning enthusiasts” and the “already tanned” showed a skin microbiota depleted in Proteobacteria.
While this reduction in diversity disappeared over time, and was non-existent by D28, the finding is important.
Skin microbiota also influenced by gut microbiota
Acne, atopic dermatitis, psoriasis, rosacea... many skin diseases are linked to an imbalance ( (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232. ) ) not only in the skin microbiota, but also in the gut microbiota. In fact, there is constant communication between the skin and these two microbial communities. This is the famed gut-skin axis 2. But what are the mediators?
Studies have shown that certain metabolites produced by the gut microbiota, known as short-chain fatty acids ( (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) ), are capable of diffusing into the body and acting on the skin 3. Acetate and propionate, for example, are thought to have an anti-inflammatory effect, while propionic acid is thought to act against certain staphylococci responsible for skin infections.
Potentially harmful changes in skin microbiota
Changes in the Proteobacteria content of the skin microbiota have already been observed in people suffering from psoriasis, eczema, and diabetic foot ulcers.
Studies have also shown that a higher skin density of Proteobacteria is associated with better protection against allergy-related skin inflammation.
These data therefore suggest that a Proteobacteria imbalance in the skin of those who tend to expose themselves to a lot of sun may lead to a deterioration in health.
Proteobacteria: harmful or beneficial?
Proteobacteria do not always get good press. You may have heard of Escherichia coli or Salmonella, which are responsible for infections. Like all bacterial groups, Proteobacteria include some beneficial bacteria, others that are more harmful, and some opportunistic bacteria that help the microbiota when it is healthy, but become harmful when the microbiota presents a dysbiosis 4. For example, Roseomonas mucosa, a skin bacterium belonging to the Proteobacteria group, is known to fight certain skin pathogens 4,5. It’s all about balance!
Admittedly, this study has a number of limitations (small number of volunteers, women overrepresented, only indirect measurement of sun exposure, etc.) and its findings need to be confirmed by larger-scale studies.
However, it does open up the possibility of one day using products based on certain beneficial bacteria (probiotics) to limit the deterioration of the skin microbiota during sun exposure.
Probiotics
1. Willmott T, Campbell PM, et al. Behaviour and sun exposure in holidaymakers alters skin microbiota composition and diversity. Front Aging. 2023 Aug 8;4:1217635.
2. O'Neill CA, Monteleone G, et al. The gut-skin axis in health and disease: A paradigm with therapeutic implications. Bioessays. 2016 Nov;38(11):1167-1176.
