The bacteria that live on your skin could be playing a role in protecting you from the sun’s harmful UV rays, scientists have discovered.
In response to solar ultraviolet radiation, our skin cells produce a molecule that, it turns out, is gobbled up by some species of bacteria that live on our skin. In doing so, they eliminate this substance, which is associated with some of the harmful effects that come with repeated sun exposure.
“We have known for a long time that UV radiation modulates immune responses directed against environmental antigens on the surface of the skin and, more recently, that the skin microbiome also plays a role in regulating these responses,” says lead author VijayKumar Patra, a biotechnologist from the University of Lyon.
“What intrigued us was the idea that certain microbes could be actively involved in or even interfere with UV effects.”
The researchers specifically tested in vitro bacteria, as well as those found on the skin of mice, for their responses to UVB, the kind of radiation that leads to sunburn.
They found certain species of bacteria, commonly found on the surface of humans and rodents alike, can break down a molecule that appears to be involved in skin cancer.
That molecule, cis-urocanic acid, is produced when another molecule in the outermost layer of skin – trans-urocanic acid – is hit with ultraviolet rays.
Previous studies have found cis-urocanic acid suppresses our skin cells’ immune systems by binding to serotonin receptors. There are concerns that this, along with the molecule’s ability to kick-start oxidative DNA damage, contributes to the development of skin cancer.
Somewhat paradoxically, researchers have also found that if cis-urocanic acid is injected into a skin tumor, it can actually have the opposite effect, acidifying the tumor’s normally neutral core and killing those cells.
Basically, cis-urocanic acid isn’t always a villain, but if it builds up around healthy cells, it can be bad news. That’s where the bacteria come in.
The researchers found common skin bacteria like Staphylococcus epidermidis can actually digest cis-urocanic acid using an enzyme called urocanase. This suggests our skin’s microbiome may be regulating the way UV exposure affects our bodies long-term.
“This is the first time we have demonstrated a direct metabolic link between UV radiation, a host-derived molecule, and bacterial behavior that affects immune function,” says skin immunologist Marc Vocanson, from the International Center for Research in Infectiology in France.
“As interest grows in both microbiome research and personalized medicine, understanding these microbe-host interactions could reshape the way we think about sun protection, immune diseases, skin cancer, or even treatments like phototherapy.”
When UVB sunscreens were first invented in 1928, by Australian chemist Milton Blake, very little was known about the microbiome, a term which was only coined in 2001.
These bacteria obviously can’t handle the job of sun protection all on their own – which is why people still get skin cancer when they ignore the sun safety measures recommended by health experts – but now that we know what these microbes are doing, we might be able to find ways to use this to improve skincare.
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“These findings open the door to microbiome-aware sun protection, where we not only protect the skin from UV radiation, but also consider how resident microbes can alter the immune landscape after exposure,” says photodermatologist Peter Wolf, from the Medical University of Graz, Austria.
He thinks treatments applied directly to the skin may one day be used to enhance or minimize the cis-urocanic acid metabolisms of these microbes to achieve desired outcomes in clinical treatment.
This could be useful, for instance, during phototherapy, in which ultraviolet light is used to treat conditions like acne, eczema, psoriasis and vitamin B deficiency. Removing the bacteria prior to these treatments could enhance their effects.
In the other direction, products that encourage the growth of S. epidermidis, or contain the urocanase enzymes, could potentially help protect the skin’s immune system, which may reduce the chances of skin cancer.
Of course, because these findings are based on test-tube experiments and the skin and microbiomes of mice, all these human applications are still speculative. Far more research is needed before any burgeoning ‘urocanase-enriched sunscreen’ products can earn the scientific seal of approval.
This research was published in the Journal of Investigative Dermatology.
