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How do the sun and sunscreens affect the skin microbiome?

Sun exposure and the use of sunscreens have a significant impact on the skin's microbiome, the delicate ecosystem of micro-organisms that protects and keeps our skin healthy. While UV rays can alter microbial composition, sunscreens play an essential role in protecting us from skin damage.

Qu’est-ce que le microbiome cutané ?

The sun and the microbiome play a crucial role in the well-being of our skin. The sun, a source of vitamin D, promotes intestinal health and strengthens our immune system.

The cutaneous microbiome represents all the genes of the micro-organisms residing on our skin. Yes, our skin is home to a multitude of micro-organisms, including bacteria, fungi, viruses, mites and archaea. These organisms make up the cutaneous microbiota, symbolizing the variety of species occupying our epidermis as well as our sweat, sebaceous and hair glands.

This microbiome is personal and unique to each individual. It is influenced by many factors, including :

  • our genes
  • our diet
  • our lifestyle
  • our stress levels
  • our hygiene practices
  • the use of medicines and cosmetics
  • interactions with other people
  • It also differs from one area of the body to another, influenced by pH, temperature, humidity and the secretion of sebum and sweat.

The cutaneous microbiome therefore refers to all the microscopic organisms present on our epidermis, essential to our skin’s balance, protection against harmful elements and localized immunity.

women skin

Its origin

It begins to form as soon as we are born. Through contact with our mother and our environment, it continues to develop and change throughout our lives, particularly at key stages such as :

  • Puberty
  • adulthood
  • Ageing

Its role

The role of the cutaneous microbiome is vital to the health of our skin and our skin in general. It maintains what is known as skin homeostasis, ensuring the balance and proper functioning of our skin. It acts as a solid skin barrier to protect us from external aggressions, and plays a beneficial role in local immunity by preventing colonization by pathogens in a number of ways:

  • by producing antimicrobial agents,
  • regulating inflammatory reactions
  • by interacting with our skin’s own immune cells.
  • Its effects don’t stop there, however, influencing our intestinal microbiota, as well as our nervous, endocrine and metabolic systems.

What are the effects of sun exposure on the skin microbiome ?

Extensive exposure to the sun has a variety of effects on the skin microbiome. On the one hand, it promotes the synthesis of vitamin D, which is beneficial to our intestinal flora and immune system. On the other hand, it can unbalance and alter the diversity of our skin microbiome by modifying the distribution of certain bacteria.

Too much UV exposure can reduce our skin’s ability to protect itself from the sun, which is why it’s so important to prepare our skin for summer. This will increase the number of bacteria present in the skin’s microbiota.

For example, exposure to UV rays (UVA/UVB) can lead to an increase in cyanobacteria, Fusobaacterium and Verrucomicrobia populations, while the Lactobacillus and Pseudomonas populations tend to decrease.

uv rays

All these changes in the bacterial flora can have repercussions on the health of our skin, as bacteria play a crucial role in immunity, inflammation and protection against pathogens.

Proteobacteria, among the most abundant on healthy skin, are particularly sensitive to UV light. Even brief exposure can reduce their number and diversity.

An imbalance in proteobacteria, including families such as the Oxalobacteraceae , is linked to skin conditions such as dermatitis, psoriasis, eczema and diabetic foot ulcers.

These bacteria have anti-inflammatory and protective properties for the skin, so their depletion can encourage the proliferation of pathogens and contribute to skin imbalance.

The impact of the sun on the skin’s microbiota is notable, but the skin tends to quickly return to equilibrium after a period without intense sun exposure. It is therefore essential to preserve the cutaneous microbiome by limiting long exposures and using an appropriate sun cream. We’ll explore the impact of sunscreens on the cutaneous microbiome in the next section, along with advice on how to choose a sunscreen that respects our microbial environment.

What impact do sunscreens have on the cutaneous microbiome ?

Sunscreens play an important, even essential role in protecting our skin from the harmful effects of the sun. They contain UV filters, which can be divided into two categories:

  • Mineral filters
  • Chemical filters
  • each acting respectively by reflecting or absorbing ultraviolet rays.

However, the impact of these UV filters on the cutaneous microbiome raises important questions.

Some research suggests that sunscreens may alter the composition and diversity of skin bacteria. More specifically, those containing nanoparticles of zinc oxide (ZnO) or titanium dioxide (TiO2), known as mineral filters, could exert an antimicrobial effect, either by killing or inhibiting the growth of certain types of bacteria.

skin solar cream

The mechanisms of action of these nanoparticles towards bacteria could involve the production of reactive oxygen species (ROS), which damage the vital components of bacteria, and the release of metal ions, including zinc ions (Zn2+), disrupting the functioning of bacteria until they die.

This antimicrobial activity raises concerns about its impact on the skin microbiome. Although available studies are sometimes contradictory and remain limited, some have revealed that formulas containing ZnO or TiO2 nanoparticles reduce the diversity and quantity of beneficial bacteria such as proteobacteria, essential to skin health.

However, further research and studies show that nanoparticles have no significant effect on the skin microbiome, compared to nanoparticle-free formulas. Caution must therefore be exercised when interpreting these results, taking into account factors such as skin type, application, frequency of use, duration of exposure to the sun and climate.

In short, while sunscreens remain essential for protection against the sun’s dangers, their effect on the cutaneous microbiome, the pillar of skin health, should not be overlooked. In some cases, they can even disrupt the skin’s defense against external aggression. It is advisable to choose products adapted to your skin type and specific needs. It’s also advisable to use sun creams sparingly, in conjunction with other sun protection methods such as covering clothing, hats and sunglasses, and avoiding exposure during peak sunshine hours.

SPF day care

SPF skincare is often the solution we turn to, but it’s essential to understand why some experts advise against its use. The chemical filters in these products can penetrate the skin and cause allergic reactions or hormonal imbalances. It is often preferable to turn to a natural alternative containing postbiotics and adapted filters.

regenerating oil

[MY] REGENERATING OIL 30ML is precisely designed to help maintain the balance of the skin’s microbiome.


We have been able to explore the impact of the sun and sunscreens on skin microbiome. We have learned that the sun can have ambivalent effects on the microbiome, depending on the intensity and duration of exposure. We’ve learned that sunscreens can sometimes alter the composition and diversity of bacteria beneficial to our epidermis.

So how do you expose yourself to the sun while taking care of your skin’s microbiome? A cautious and conscious approach is recommended. Avoid prolonged exposure to the sun, and choose a sun protection product suited to your skin type, level of exposure and sensitivity to product ingredients.

Taking care of your skin’s microbiome is essential. How? By adopting a balanced diet, practicing gentle hygiene and supporting your skin’s flora with probiotics and prebiotics. Adopting these measures means you can enjoy the sun with peace of mind, without compromising the health of your skin and body.


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