Your Skin Microbiome & The Sun

Should we soak up the sun for its health benefits, protect our skin from it at all costs? Is sunscreen the one skincare product that everyone truly needs, or is it just adding chemicals to our skin? What’s the truth in a world full of conflicting information?

We’ve tackled some of these questions before, diving into the science of the pros and cons, including:

The Sun Exposure Dilemma

…and:

Who Screens The Sunscreens?

And now, today, we’re going to be talking about some entirely new science!

An extra layer of protection

Who would win:

• a 4,600,000,000-year-old ongoing nuclear fusion event whose superheated plasma is held in place by its own immense gravity well, or
• some single-celled organisms that were born a few minutes ago?

The answer is that the latter can, in fact, help to protect us against the former.

Re “born a few minutes ago”: if you’ll pardon the rhetorical device (per “born yesterday” etc), what we mean here is that the life cycle of such microbes is very short, so while your microbiome is as old as you are (albeit in ship of Theseus sort of way), any individual living microbes will not be more than some minutes old.

We mention this not as a matter of mere interesting trivia, but rather because it has practical implications: when it comes to our microbiome (or microbiomes, depending on whether we want to count different sites on/in our body separately, as is often useful, even if technically they all do interact with each other thus they could be considered one big diverse microbiome too), it is a living community that needs to be given the right circumstances to perpetuate and favorably mutate itself constantly.

It’s not something that can be optimized and then just taken for granted. Because sure, given good conditions, an optimized microbiome will then continue to self-perpetuate, mutate as it goes, and by virtue of natural selection, continue to persist against threats. But if not given good conditions? You could wreak havoc with it and take weeks or more for it to recover. And if those bad conditions are chronic, it might never recover.

So, more on healthy microbiome curation later, but first, the exciting new science!

Teaser:

❝This pivotal study shows that microbial communities are not passive victims of environmental stress but dynamic regulators of immune responses, capable of metabolizing UV-induced skin products such as cis-urocanic acid. This newly uncovered role of microbial metabolism in modulating UV tolerance reshapes our understanding of the skin barrier — not just as a structural shield but as a metabolically active, microbially regulated interface. With increasing concerns about UV exposure, skin aging, and cancer, a deeper understanding of this axis offers promising avenues for therapy and prevention.❞

~ Dr. Anna Di Nardo (not one of the study authors, just a physician-scientist expert in the field)

In few words: researchers have discovered that certain bacteria on our skin help protect us from sun damage and also play a role in controlling our immune system.

How this works: when sunlight (especially UVB rays) hits our skin, it changes a natural chemical there (namely: trans-urocanic acid) into a dangerous form (namely: cis-urocanic acid), which also incidentally weakens the immune system. Some skin bacteria can break down this harmful chemical with an enzyme they produce (namely: urocanase). This enables the skin to better manage its skin exposure; specifically, controlling responses to UV exposure.

This is exciting, because it’s the first evidence of a direct link between UV rays, a skin molecule, and microbial activity affecting health outcomes, not just passively, but through active metabolism.

You can read the paper itself here:

Urocanase-positive skin resident bacteria metabolize cis-urocanic acid and in turn reduce the immunosuppressive properties of UV radiation

Great! How can we make use of this information?

Per the researchers’ conclusions, these insights could change how we think about sun protection, immune-related skin diseases, skin cancer, and more. The note also that future sun care could include microbiome-aware treatments that adjust bacterial metabolism to improve skin health after sun exposure.

And in the meantime? Generally speaking when it comes to microbiome health (any microbiome; gut, oral, skin, etc), a good rule of thumb is “if in doubt, just leave it alone and let it do its thing”.

This might sound like passive “do-nothing” advice, and in a way it is, but a lot of people don’t do nothing, and when it comes to the skin microbiome in particular, it’s very common for people to invest a lot of time and energy into killing everything that moves, so the advice here is “stop doing that”.

Which doesn’t mean you mustn’t wash; by all means, feel free to wash, but gently.

We’ve written a bit about this before:

• Should You Shower Daily?
• Body Scrubs: Benefits, Risks, and Guidance
• Dealing With Back Acne

And if you already have sun-damaged skin…

Undo The Sun’s Damage To Your Skin

Take care!