Spending time enjoying the sunshine has been a tonic in the Northern hemisphere during COVID-19 lockdown. As we edge into summer, we have relished the changes in light, the comforting warmth and nature responding gloriously. Those first rays of summer can feel blissful on the skin, too, but we know that we need to protect it from UV rays to reduce our risks of skin cancer and sun damage. Did you know the sun can also affect your skin microbiome?
UV radiation can change the balance of microbes in the skin, potentially interrupting the skin’s delicate homeostasis  . When our skin microbiome is knocked out of kilter, inflammation, and associated conditions, such as psoriasis and eczema, can occur along with more serious effects.
The microbiome is an essential part of our skin’s immune response. The skin is our first line of defence against pathogens, and its microbes deter them by jostling with them for space and making antipathogenic substances . Emerging science suggests the microbiome even plays an important role in helping mitigate the negative effects of sun overexposure on our skin and may suppress tumour growth  . The future of sun care could lie in harnessing the power of the microbes that do this.
Meanwhile, seeking shade and covering our skin with hats and clothing is an easy way to help protect our microbiomes from the sun’s rays. But what about sunscreen? Is it friend or foe to our microbial helpers?
The truth is that we don’t know for sure how all the different products out there might affect our skin microbiomes, which in any case are all unique. But the good news is that there is no evidence that regular sunscreen use is detrimental to the microbiome, and the British Association of Dermatologists continues to recommend those with fair skin always apply at least SPF-30 sunscreen before going out .
“Sunscreen is going to make a somewhat different environment on the skin, and that will likely change the surface bacteria,” says Richard Gallow, chairman of the Department of Dermatology at the University of California, San Diego. “But over a long haul, there’s no evidence to suggest that sunscreen is bad for you because it hurts your bacteria.”
This is in large part because the anatomy of the skin has evolved to protect its microbiome. The millions of follicles in our skin contain glands that provide protected niches for our microbes. “They’re actually down deep, kind of in the dark,” says Gallow, reassuringly. Even when we use antimicrobial products to wash bacteria off the surface on our skin, within minutes those bacteria that are living down deeper repopulate the surface, such as Cutibacterium acnes – a bacterium often associated with acne.
There’s no doubt that UV protection is essential for maintaining skin health, especially for reducing the risk of developing skin cancer – the most common type of cancer in the UK . Due to Covid-19, our habits have changed significantly so whether spending more time inside during the lockdown or making the most of the sunny weather, it is crucial to incorporate a high factor sunscreen into your skincare regime to ensure you are protected.
While humans can tolerate small doses of sun (the precise dose differs according to skin type), Gallow suspects the skin microbiome does a better job of resisting sun damage than human cells, which are constantly accumulating mutations from it. That’s not to say that the recommended use of sunscreen isn’t vital for broader health and protection against harmful rays, but sticking to a sensible sunscreen routine will maintain your unique microbial balance.
“If you are practical about this and look at the data,” he says, “those everyday sun exposures that you’ve had throughout your whole life have actually shaped your microbiome to be what it is today. Now, over long periods of time, if you dramatically change your behaviours, your skin microbiome will change.”
Allergies and individual sensitivities aside, the one type of sunscreen to avoid is anything with an old-school high oil content. “These products can plug the pores and then lead to acne-like eruptions and so forth because of the way that changes the microbial community,” says Gallow. Luckily, however, oily formulations are no longer the norm. Modern sunscreens come in an array of light, skin-friendly formulations to suit different skin types and requirements.
Increasingly, skincare products, including sunscreens, are billing themselves as microbiome friendly. The South African plant-based brand Esse, for instance, says its sunscreen has no significant effect on the microbiome. The US-based vegan company, Pacifica, offers “probiotic” sunscreen, which contains lysates – the healthy fermentation chemicals left behind by live bacteria.
There are no clinical trials proving any benefits for the microbiome of products like these, but they could in theory offer an advantage. “If a product has something that perhaps slightly promotes the survival of beneficial bacteria, that theoretically would be good for you,” says Gallow. “But the good news is that your skin is doing the most work to protect your bacteria.”
References: Patra et al, 2016, 523 Ultraviolet-radiation (UV-R) affects the skin microbial load and influences the expression of antimicrobial peptides (AMPs) in mice Burns et al, 2018, Ultraviolet radiation, both UVA and UVB, influences the composition of the skin microbiome Janeway et al, 2001, Immunobiology: The Immune System in Health and Disease. 5th edition – The front line of host defense. Patra et al, 2019, Skin microbiome modulates the effect of ultraviolet radiation on cellular response Nakatsuji et al, 2018, A commensal strain of Staphylococcus epidermidis protects against skin neoplasia British Association of Dermatologists, 2020, Sun protection advice for the UK during lockdown