How can the skin microbiome be preserved?

The cutaneous microbiome refers to the community of micro-organisms that inhabit the surface of the skin and the activities they carry out there.

This microscopic ecosystem, unique to each individual, is as complex as a forest ecosystem: it varies according to body region, pH, sebum production sebum, but also according to age, sex, environment or lifestyle. Oily areas such as the face or back harbour more Cutibacterium spp., while moist areas such as the axillary folds favour Corynebacterium spp. and Staphylococcus spp., whereas dry areas, such as the forearms, host a more diverse flora. These microorganisms actively contribute to the functioning and overall health of the skin.

Indeed, the cutaneous microbiome protects, regulates and repairs the skin. It acts as a living barrier that prevents pathogen colonisation 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. Concurrently, the skin microbiome contributes to maintaining the skin’s pH, hydration and hydrolipidic film of the skin. An imbalance, in other words dysbiosis, makes the skin more vulnerable to redness, irritation, and skin conditions such as acne or eczema.

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

Maintain a regular sleep–wake cycle.

As with the whole organism, the skin follows a 24-hour circadian rhythm that regulates various biological functions, such as sebum production, cell renewal, DNA repair and immunity. During the day, the skin defends itself against external aggressors and produces more sebum, while at night it actively regenerates: keratinocyte and fibroblast proliferation intensifies, the permeability of the skin barrier increases and blood flow improves. The skin microbiome also follows these circadian fluctuations. A study conducted with four participants showed that certain bacterial families, such as the Propionibacteriaceae or the Paracoccaceae, exhibit variations in abundance between morning and evening, reflecting this synchronisation with the biological rhythm.

When the circadian rhythm is disrupted—through late bedtimes, insufficient or irregular sleep—microbial diversity diminishes and the skin barrier becomes more vulnerable. These imbalances promote inflammation, via an increase in pro-inflammatory cytokines, and compromise hydration as well as the hydrolipid film. Regular, sufficient sleep that aligns with day/night cycles is therefore essential to maintain a stable and protective microbiome.

Maintain a balanced diet.

Diet plays an important role in the equilibrium of the skin microbiome, via the gut–skin axis. This bidirectional communication system links the gut microbiota, the immune system and the skin. The principle is as follows: metabolites produced by intestinal bacteria influence inflammation, oxidative stress and the skin’s barrier function. In turn, the state of the skin and its microbiota can also affect intestinal physiology.

Thus, a diet rich in saturated fats and high glycaemic index sugars is associated with microbial imbalances and increased inflammation. Conversely, diets high in fibre, antioxidants and unsaturated fatty acids promote enhanced microbial diversity and more balanced skin. Fermentable fibres, for instance, stimulate the production of short-chain fatty acids like 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 the maintenance of skin structure.

Engage in regular physical activity, but in a balanced manner.

Besides being beneficial for the body and mental well-being, physical activity indirectly influences the skin microbiome by enhancing blood circulation and perspiration, both of which modify the skin’s microbial environment. However, although exercise generally promotes better oxygenation and reduces oxidative stress, certain contact sports, such as wrestling or rugby, may alter microbiome balance by exposing the skin to opportunistic microorganisms, such as Staphylococcus aureus or Tinea corporis, increasing the risks of bacterial or fungal infections.

Research has also shown that certain specific sporting environments, such as swimming pools, can alter the composition of the skin microbiota. Researchers observed that chlorine, although antimicrobial, did not eliminate the presence of 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 from the Pseudomonadaceae family, known for their ability to colonise 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 recolonisation.

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

Use hygiene products that respect the skin microbiome.

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 for keeping microbial populations in check, from sterilisation, 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 encourage the proliferation of opportunistic bacteria.

Studies have shown that handwashing alters the superficial bacterial composition without affecting the overall diversity of the 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 susceptible to colonisation 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 quality of water and detergent use impact the skin microbiome. Hard water, rich in calcium and magnesium ions, promotes the precipitation of surfactants such as the sodium lauryl sulfate, already controversial, which remains on the skin for longer and damages the skin barrier. This phenomenon raises the pH, disturbs the lipids of the stratum corneum and decreases the content of natural moisturising factors (NMF), leading to dysbiosis and skin dryness. Opting for mild, sulphate-free cleansers, limiting prolonged exposure to hard water, and favouring physiologically pH-balanced formulations thus helps to 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 garments, and thus with an array of textile fibres, chemical additives and detergent residues. This prolonged proximity creates an ecosystem at the interface of the cutaneous microbiome and the “textile microbiome”. This contact influences the composition of the skin microbiota. The textile industry often incorporates antimicrobial agents, such as silver nanoparticles, to curb odour development. However, these compounds trigger an increase in monounsaturated fatty acids associated with a higher abundance of Cutibacterium. In contrast, natural fibres such as raw linen can inhibit the growth of S. aureus and S. epidermidis, while sterile extracts of linen and cotton modulate their capacity to form biofilms, protective structures that favour their persistence on the skin surface.

A recent study sought to gain a better understanding of how fabric extracts influence bacterial growth and biofilm formation. To this end, extracts from various textiles were incubated for 24 hours in a culture medium at 37 °C before introducing S. aureus and S. epidermidis. Although overall bacterial growth did not vary by fabric type, the biofilms, by contrast, were strongly inhibited : reductions ranged from 47% to 74% for S. aureus, and up to 71% for S. epidermidis. These results suggest that certain textile fibres release compounds capable of reducing bacterial adhesion without directly affecting microbial growth, a effect potentially double-edged, capable of disrupting the stability of the skin microbiome while limiting pathogenic colonisation.

To preserve the balance of the cutaneous microbiome, it is therefore recommended to opt for untreated natural fibre garments and to favour laundry detergents free from antimicrobial agents and synthetic fragrances.

Reducing one’s exposure to pollutants.

Living in an urban environment daily 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 comprise this ecosystem. Over the long term, chronic exposure can disrupt the microbiome’s ability to metabolise lipids, carbohydrates and amino acids, while increasing the pathogenic potential of certain bacterial species.

Polycyclic aromatic hydrocarbons, notably arising from vehicular or 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 a dysregulation in the breakdown of aromatic compounds and an increase in bacterial virulence. Nitrogen dioxide (NO₂) also acts as a dysbiosis factor. Recent research has revealed that certain commensal species, such as Corynebacterium tuberculostearicum and S. capitis, are particularly sensitive, whereas S. aureus, more resistant, tends to become dominant in this oxidative environment. This differential selection promotes a loss of microbial diversity and opportunistic colonisation, often associated with chronic inflammatory skin conditions.

Cigarette smoke represents another significant source of oxidative and chemical stress to the skin. Indeed, cigarettes harbour various types of bacteria, such as Bacillus, Clostridium or Klebsiella, which can be pathogenic. Smoking thus alters microbial β-diversity, meaning the overall structure of bacterial communities, by promoting the loss of beneficial species and the proliferation of taxa tolerant to combustion. Some of these alterations, however, appear reversible after cessation of tobacco, suggesting a capacity for resilience in the cutaneous microbiome once the source of assault is removed.

Practical advice :

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

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

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

Protecting your skin from solar radiation.

Exposure to ultraviolet radiation is well known for its harmful effects on the skin, ranging from inflammation to photoageing, including a heightened risk of skin cancer. However, the impact of UV radiation on the skin microbiota is less frequently addressed, despite being far from negligible.

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 may promote skin alterations and increase the risk of inflammatory diseases such as psoriasis or eczema. Notably, the work carried out by Yusuf and his team can be cited, in which they 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 presented in the following table.

It should be noted that micro-organisms’ responses to UV radiation vary according to their structural characteristics. Gram-positive bacteria appear more resistant to UV-induced oxidative stress than Gram-negative bacteria, thanks to their thicker cell walls, which filter out part of the rays. This differential sensitivity explains why some bacterial groups decline following sunlight exposure, while others persist or adapt.

Protecting your skin with sun cream, limiting periods of intense exposure and wearing covering clothing contribute not only to preventing photoageing and skin cancers, but also to maintaining the balance of the skin’s microbiota.

• GONTIJO FILHO P. P. & al. Changes in hands microbiota associated with skin damage because of hand hygiene procedures on the health care workers. American Journal of Infection Control (2009).

• VISSERS M. C. M. & al. The roles of vitamin C in skin health. Nutrients (2017).

• YUSUF N. & al. Ultraviolet radiation, both UVA and UVB, influences the composition of the skin microbiome. Experimental Dermatology (2018).

• GROBOILLOT A. & al. Deleterious effects of an air pollutant (NO2) on a selection of commensal skin bacterial strains, potential contributor to dysbiosis? Frontiers in Microbiology (2020).

• RINALDI F. & al. Effect of commonly used cosmetic preservatives on skin resident microflora dynamics. Scientific Reports (2021).

• LEUNG M.H.Y. & al. Diurnal variation in the human skin microbiome affects accuracy of forensic microbiome matching. Microbiome (2021).

• KIMBALL A. B. & al. Yin and Yang of skin microbiota in “swimmer acne”. Experimental Dermatology (2022).

• FEUILLOLEY M. G. J. & al. Cotton and flax textiles leachables impact differently cutaneous Staphylococcus aureus and Staphylococcus epidermidis biofilm formation and cytotoxicity. Life (2022).

• UBAGS N. D. & al. Skin barrier immunology from early life to adulthood. Mucosal Immunology (2023).

• PICCIONI A. & al. The impact of smoking on microbiota: A narrative review. Biomedicines (2023).

• GOMEZ-CASADO C. & al. The influence of lifestyle and environmental factors on host resilience through a homeostatic skin microbiota: An EAACI Task Force Report. European Journal of Allergy and Clinical Immunology (2024).

• YADAV H. & al. Microbiome and postbiotics in skin health. Biomedicines (2025).