How can we preserve the skin microbiome?

The cutaneous microbiome refers to the community of microorganisms that live on the skin’s surface and the activities they carry out there.

This microscopic ecosystem, specific to each individual, is as complex as a forest ecosystem: it varies by body site, pH, production of sebum, but also by age, sex, environment, or lifestyle. Oily areas like the face or back harbor more Cutibacterium spp., while moist areas such as the underarm folds favor Corynebacterium spp. and Staphylococcus spp., whereas dry areas, such as the forearms, host a more diverse flora. These microorganisms actively contribute to the overall function and health of the skin.

Indeed, the skin microbiome protects, regulates, and repairs the skin. It acts as a living barrier that prevents pathogen colonization by occupying space and producing natural antimicrobial molecules. It also modulates the skin’s immune response: certain commensal bacteria, such as Staphylococcus epidermidis, stimulate the production of antimicrobial peptides and promote immune tolerance, thereby limiting inflammatory reactions. At the same time, the skin microbiome contributes to maintaining skin pH, hydration, and the hydrolipid film of the skin. An imbalance, i.e. dysbiosis, leaves the skin more susceptible to redness, irritation, and dermatoses such as acne or eczema.

The skin microbiome is a delicate balance influenced by numerous internal and external factors, such as hygiene, cosmetic routines, skincare products, and stress. Fortunately, certain habits help maintain a stable and resilient microbiome.

Maintain a regular sleep-wake cycle.

Like the body as a whole, the skin follows a 24-hour circadian rhythm that regulates various biological functions, including sebum production, cell turnover, DNA repair, and immunity. During the day, the skin defends against external stressors and produces more sebum, whereas at night it actively regenerates: keratinocyte and fibroblast proliferation intensifies, the skin barrier’s permeability increases, and blood circulation is enhanced. The skin microbiome also follows these circadian oscillations. A study conducted with four individuals showed that certain bacterial families, such as the Propionibacteriaceae or the Paracoccaceae, exhibit fluctuations in abundance between morning and evening, reflecting this synchronization with the biological rhythm.

When the circadian rhythm is disrupted — for example by late bedtimes, insufficient, or irregular sleep — microbial diversity decreases and the skin barrier becomes more vulnerable. These imbalances promote inflammation, via an increase in pro-inflammatory cytokines, and compromise hydration and the hydrolipidic film. Regular, sufficient sleep aligned with the day/night cycle is therefore essential to maintain a stable, protective microbiome.

Maintain a balanced diet.

Diet plays a significant role in maintaining the balance of the skin microbiome, via the gut–skin axis. This bidirectional communication system links the gut microbiota, the immune system, and the skin. In essence, metabolites produced by intestinal bacteria influence inflammation, oxidative stress, and the skin’s barrier function. Conversely, the condition of the skin and its microbiome can also impact intestinal physiology.

Thus, a diet rich in saturated fats and high-glycemic-index sugars is associated with microbial imbalances and heightened inflammation. In contrast, the diets rich in fiber, antioxidants, and unsaturated fatty acids promote improved microbial diversity and more balanced skin. Fermentable fibers, for example, stimulate the production of short-chain fatty acids such as butyrate, which can strengthen the epidermal barrier and modulate keratinocyte activity. Studies have also shown that an adequate intake of essential micronutrients, such as the vitamin C, contributes to protection against oxidative stress and to the maintenance of skin structure.

Engage in regular physical activity while maintaining balance.

In addition to benefiting the body and mood, physical activity indirectly influences the skin microbiome by stimulating blood circulation and sweating, factors that alter the skin’s microbial environment. However, while exercise generally promotes better oxygenation and reduces oxidative stress, certain contact sports, such as wrestling or rugby, may disrupt microbiome balance by exposing the skin to opportunistic microorganisms like Staphylococcus aureus or Tinea corporis, increasing the risks of bacterial or fungal infections.

Studies have also shown that certain specific sports environments, such as swimming pools, can alter the composition of the skin microbiota. Researchers observed that chlorine, although antimicrobial, did not eliminate acne in some swimmers. After one hour of immersion, coproporphyrin III, a marker of the abundance of Cutibacterium acnes, the bacterium primarily involved in acne, decreased significantly. However, this alteration was accompanied by an increase in bacteria of the family Pseudomonadaceae, known for their ability to colonize moist environments. Thus, despite the reduction of C. acnes, the overall composition of the skin microbiota remained unbalanced. The authors note that this imbalance was more pronounced in swimmers who already had acne, suggesting a specific vulnerability to pathogenic recolonization.

To preserve the diversity of the skin microbiome while enjoying the benefits of exercise, it is essential to adopt good hygiene practices, notably by showering after each session with a gentle cleanser and properly drying your skin after exercise.

Use hygiene products that respect the skin microbiota.

Hygiene habits directly influence the composition of the skin microbiome, and their impact depends less on frequency than on the nature of the products used. Indeed, it is essential to distinguish cleanliness, which allows you to keep microbial populations under control, from sterilization, which indiscriminately eliminates both pathogenic and protective microorganisms. Overly aggressive hygiene practices, particularly the repeated use of disinfectants or alkaline soaps, can disrupt the skin microbiome and promote the proliferation of opportunistic bacteria.

Studies have shown that handwashing alters the superficial bacterial composition without affecting the overall diversity of deeper layers, indicating that the resident flora remains relatively stable. However, in healthcare professionals subjected to frequent washing, the skin becomes more prone to irritation and to colonization by resistant bacteria such as Staphylococcus aureus. Alcohol-based antiseptics, ethanol, or povidone-iodine rapidly reduce the number of resident species, while the most resistant members such as Propionibacteriaceae, retain a competitive advantage.

Finally, the water quality and the use of detergents impact the skin microbiota. Hard water, rich in calcium and magnesium ions, promotes the precipitation of surfactants such as sodium lauryl sulfate, already controversial, which remains on the skin longer and impairs the skin barrier. This effect increases pH, disrupts the lipids of the stratum corneum, and reduces the content of natural moisturizing factors (NMF), leading to dysbiosis and skin dryness. Opting for gentle sulfate-free cleansers, limiting prolonged exposure to hard water, and favoring formulations with a physiological pH thus help preserve the diversity and stability of the skin microbiome.

Opt for clothing and laundry detergents that respect the skin microbiome.

The skin is in constant contact with clothing, and therefore with a range of textile fibers, chemical additives, and laundry residues. This prolonged proximity creates an ecosystem at the interface of the skin microbiome and the "textile microbiome". This contact influences the composition of the skin microbiota. However, the textile industry frequently incorporates antimicrobial agents, such as silver nanoparticles, intended to limit odor development. Yet these compounds induce an increase in monounsaturated fatty acids associated with a greater presence of Cutibacterium. In contrast, natural fibers such as raw linen can inhibit the growth of S. aureus and S. epidermidis, while sterile linen and cotton extracts modulate their ability to form biofilms, protective structures that promote their persistence on the skin surface.

A recent study sought to better understand how fabric extracts influence bacterial growth and biofilm formation. For this purpose, extracts from various textiles were incubated for 24 hours in culture medium at 37 °C before introducing S. aureus and S. epidermidis. While overall bacterial growth did not vary by fabric type, the biofilms were strongly inhibited: between –47% and –74% for S. aureus, and up to –71% for S. epidermidis. These findings suggest that certain textile fibers release compounds capable of reducing bacterial adhesion without directly affecting microbial growth, an effect potentially acting as a double-edged sword that could disrupt skin microbiome stability while limiting pathogenic colonization.

To maintain the balance of the skin microbiome, it is therefore recommended to choose clothing made from untreated natural fibers and to use laundry detergents that are free of antimicrobial agents and synthetic fragrances.

Reduce your exposure to pollutants.

Living in an urban environment exposes the skin to a complex cocktail of atmospheric pollutants. These contaminants interact directly with the epidermis, altering the stability of the microbiome and the metabolic functions of the bacteria that compose this ecosystem. Over the long term, this chronic exposure can disrupt the microbiome’s ability to metabolize lipids, carbohydrates, and amino acids, while increasing the pathogenic potential of certain bacterial species.

Polycyclic aromatic hydrocarbons, primarily generated by vehicle and industrial combustion, penetrate the skin and enter the bloodstream. A study has shown that prolonged exposure profoundly alters the metabolic profile of the skin microbiome, leading to dysregulation of aromatic compound breakdown and increased bacterial virulence. Nitrogen dioxide (NO₂) also acts as a dysbiosis factor. Recent work has demonstrated that certain commensal species, such as Corynebacterium tuberculostearicum and S. capitis are particularly sensitive to these conditions, while S. aureus, being more resistant, tends to become dominant in this oxidizing environment. This differential selection promotes loss of microbial diversity and opportunistic colonization, often associated with chronic inflammatory skin conditions.

Cigarette smoke constitutes another significant source of oxidative and chemical stress to the skin. Indeed, cigarettes harbor various types of bacteria, such as Bacillus, Clostridium or Klebsiella, which can be pathogenic. Smoking thus alters the β-diversity of the microbiome, that is, the overall structure of bacterial communities, by promoting the loss of beneficial species and the proliferation of combustion-tolerant taxa. Some of these alterations, however, appear reversible after the cessation of tobacco, suggesting that the skin microbiome can recover once the source of damage is eliminated.

Practical advice :

• Avoiding cigarette smoke protects not only health but also the skin microbiome.

• Wearing a mask can help protect the skin from pollution in a heavily polluted urban environment.

• Using antioxidant skincare protects the skin and its microbiome from oxidative stress.

Protecting your skin from the sun’s ultraviolet radiation.

Exposure to ultraviolet (UV) radiation is well known for its deleterious effects on the skin, ranging from inflammation to photoaging, as well as an increased risk of skin cancer. However, the impact of UV on the skin microbiota is less often discussed, even though it is significant.

Recent studies show that exposure to UVA and UVB alters the composition of the microbiota, notably disrupting populations of Proteobacteria, which are associated with protective anti-inflammatory immune responses. An imbalance in these bacteria can promote skin abnormalities and increase the risk of inflammatory diseases such as psoriasis or eczema. For example, the work conducted by YUSUF and his team tested the effects of UVA and UVB on the human skin microbiome. To this end, participants were exposed to UVA doses (22 - 47 J/cm2) or UVB (100 - 350 mJ/cm2), and samples were collected. DNA was isolated and sequenced to identify the microbial composition of each sample. The results are reported in the table below.

It should be noted that microorganisms’ responses to UV radiation vary based on their structural characteristics. Gram-positive bacteria appear more resistant to UV-induced oxidative stress than Gram-negative bacteria, owing to their thicker cell walls that filter part of the rays. This differential sensitivity explains why certain bacterial groups decline after sun exposure, while others persist or adapt.

Protecting your skin with sunscreen, limiting hours of intense sun exposure, and wearing covering clothing contribute not only to preventing photoaging and skin cancers, but also to maintaining the balance of your skin microbiota.

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