The Hidden Battle of Bacteria and the Sun on Our Skin
Every time you head to the beach or stroll under an intense sun, your skin engages in a complex series of reactions on its surface. While many might think immediately of vitamin D and sunburn , there’s a more profound microscopic struggle occurring — a fascinating ‘battle’ where the bacteria that inhabit your skin play a pivotal role. What they do is both intriguing and vital: they literally “consume” one of the most harmful effects of sunlight, modifying how our body reacts to it.
The Threat of Sunlight to Immune Defenses
To comprehend this narrative, it’s crucial to recognize that the sun does more than merely bronze our skin. Ultraviolet radiation (UV) acts as a potent switch for the immune system. When UV rays strike the skin, they transform a common molecule known as urocanic acid into its ‘twin’, cis-urocanic acid.
This new molecule, termed CIS-UA, has a singular mission: to serve as a powerful immunosuppressive agent. Essentially, it disarms skin ‘defenses,’ preventing reactive responses to sun exposure. While this can facilitate the use of phototherapy with UV light for treating inflammatory conditions like dermatitis, it also bears a downside. A lack of heightened defenses can impede the body’s ability to eliminate sun-damaged cells, which over time can possibly lead to the evolution of skin cancer.
The Crucial Role of Skin Bacteria
A study published in the Journal of Investigative Dermatology sheds light on why the immunosuppressive effect of CIS-UA in real-life environments wasn’t as potent as anticipated in controlled laboratory settings. The clue lies in the billions of microorganisms residing in our skin, collectively termed the microbiome.
In a series of experiments on animals, researchers found that exposure to UV radiation resulted in a spike in specific bacteria populations, particularly Staphylococcus epidermidis. This was not coincidental. This bacterium has a catalase-type enzyme that acts as a ‘crusher’ for CIS-UA, effectively depleting its presence.
In essence, while the sun generates this immunosuppressive molecule, our skin bacteria utilize it as a food source, reducing its levels and thereby safeguarding our defenses.
Validating the Role of Bacteria
To further substantiate this theory, researchers disinfected the skin of mice to eliminate their microbiome. When subjected to UV radiation, the immunosuppressive effect of CIS-UA escalated dramatically. Without bacteria to degrade the CIS-UA, the molecule was free to silence the skin’s defenses, increasing the risk of cancer.
However, when the bacterium Staphylococcus epidermidis was reintroduced to the skin, the skin’s defenses remained intact, confirming the role of bacteria as regulators of sunlight effects on our skin.
A New Avenue for Sun Protection
These findings are not merely intellectual curiosities; they pave the way for novel medical and cosmetic applications. For patients with conditions like psoriasis or atopic dermatitis, a straightforward intervention — disinfecting the skin prior to UV light therapy — could enhance treatment efficacy by preventing the suppression of skin defenses.
In everyday scenarios, we should focus on minimizing immunosuppression to maintain active defenses against prolonged sun exposure. Future sunscreens could not only block UV rays but also incorporate ‘probiotics’ or ingredients that nourish beneficial bacteria. This approach could bolster our natural defenses rather than relying solely on synthetic chemicals. Nonetheless, traditional sunscreen remains critical.
Bacteria: Our Unseen Allies
Often associated with disease, bacteria actually comprise approximately 100 billion microorganisms in the human body — a staggering ten times more than human cells. These microorganisms perform crucial roles, and alterations in the human microbiota are linked to severe conditions such as Alzheimer’s and depression. Recent research has unveiled another beneficial function of the bacteria living with us, indicating that they may be more allies than adversaries.
This trend in research points to a future where health entails enriching our bodies with probiotics and understanding the effects of popular diets like intermittent fasting on our microbiome. The pursuit of these insights is a priority across diverse scientific disciplines, reflecting the intricate relationship we share with these tiny organisms.
Images | CDC | Morgan Alley.