Our skin is crawling with bacteria - and that's good news
25 June 2019
By Simon Crompton
There's a war occurring on the surface of our bodies. We need bugs, mites and fungi to win it, says Simon Crompton
You have just about got used to cherishing your gut flora, but can you learn to love the bugs on your skinScience is telling us that human skin hosts a precious ecosystem of billions of bacteria, viruses, fungi — even tiny mites in our hair follicles — that are far from unhygienic. They are essential to our health.
Last month new evidence showed that "good" bacteria play a role in keeping eczema-causing bacteria in check. Dermatologists from the University of California San Diego reported that toxins produced by the skin bacterium Staphylococcus aureus (S aureus) cause skin damage, opening a way for bacteria to get in and cause an eczema flare-up. However, competing bacteria living on the skin prevent this by producing proteins that stop the S aureus bacterium from communicating its message to start secreting toxins.
"It's a battle for survival on the skin," says Richard Gallo, a professor of dermatology at San Diego, who led the research and has uncovered complex systems where skin bacteria and human cells work to benefit each other. "Human organisms, all animals, have evolved systems to help certain bacteria win that battle because these bacteria don't hurt us."
Millions of micro-organisms hold each other in a delicate balance on our skin. And although scientific understanding of skin flora lags way behind that of the gut microbiome there are indications that these bugs are vital for wellbeing. Studies have shown that animals that are artificially deprived of their microbiome have problems with their immune system.
According to Gallo, the communities of bacteria on our skin provide many benefits in return for us giving them a home. "Good" bacteria produce antimicrobial chemicals to kill competing bacteria that are more likely to cause disease. They strengthen the skin barrier to prevent water loss and the entry of harmful microbes. And they educate the immune system so that it doesn't overreact and cause skin allergies.
Research has shown that this is important for conditions such as acne, psoriasis, eczema and rosacea — and even cancer prevention. Last year a team led by Gallo found that a strain of the Staphylococcus epidermidis (S epidermidis) bacterium, commonly found on skin, produces a chemical that can inhibit the proliferation of melanoma and lymphoma cells.
Gallo became interested in this field 20 years ago when his laboratory was investigating how skin cells make antimicrobial proteins called peptides to kill harmful invaders. He discovered that the human body was not acting alone. Bacteria on the skin were producing peptides too, that work in synergy with our own.
"There's apparently been coevolution where we particularly benefit," he says. "Our conclusion is that it's appropriate to think of the bacteria almost in terms of being another of our immune cells. We have white blood cells that are there in part to kill bacteria that are trying to infect us. And then we have another kind of immune cell — it's just not human, it's certain kinds of bacteria that we harbour on our skin that kill bacteria that are trying to infect us."
What are the implications for our everyday livesProfessor Carsten Flohr, the head of population-based dermatology research at King's College London, says that most of us have a "healthy" microbiome, but problems can arise for many reasons. Sometimes it's an overreaction of our immune cells. For example, rosacea — a condition that causes redness and bumps, mainly on the face — may be provoked by an exaggerated immune response to the Demodex folliculorum mites that normally live harmlessly in skin pores feeding on dead skin and oils. Most problems, though, tend to come when we have a genetic susceptibility that weakens the skin barrier and allows bugs in or if our skin becomes less hospitable to some bacteria and the delicate balance of nature is thrown. Diversity is all.
Dry skin, Flohr says, is likely to be triggered by a genetic trait that makes some people's skin barrier weak and more likely to lose water, but skin disruption can be made worse by environmental factors. His research published in 2017 shows that babies in hard-water areas are more likely to develop eczema because hard water is alkaline while skin is naturally acidic. Reducing skin acidity (pH) causes skin barrier breakdown and encourages bacteria to thrive.
So more bugs get under the skin and the result is inflammation, itchy, dry skin and eczema. Once that has started, we can make things easier for the bad bacteria by reducing skin acidity further by using detergent-based soaps and shampoos. We shouldn't overuse products that make lots of bubbles, Flohr says, because they contain surfactants, which can weaken the skin barrier. "Fifty years ago we wouldn't have used any of these products," he says. "We would just have used bath soap and that was it." Specialist dermatologists are generally sceptical of a new wave of cosmetic products that claim to promote a "healthy" skin microbiome.
"Your microbiome is as individual to you as your fingerprints," says Catherine O'Neill, a professor of translational dermatology at the University of Manchester. "There are certainly companies which are trying to modulate the microbiome for health, but I don't know what they're trying to do because we don't know what a healthy skin microbiome looks like." However, there is the prospect of new products harnessing the power of bacteria to promote skin health. Gallo's laboratory in San Diego is using new knowledge about the skin microbiome to develop a topical cream for eczema. It contains strains of S epidermidis, a bacterium known to suppress S aureus.
In the UK, O'Neill is developing a cream for eczema based on "probiotic" gut bacteria known to prevent dangerous micro-organisms from entering the gut, bolster the cell lining of the intestines and promote healing. Her studies found that the probiotic bacteria had similar effects on the skin, strengthening the skin barrier, which can be brittle in eczema.
Such creams, she says, may have a more general cosmetic function for healthy skin too. "Our research showed there was a clear hydrating effect on the skin, which always makes it look better and plumps out fine lines. We've also got some data that strongly suggests that our bacterial extract might be able to repair some of the skin damage caused by sunlight, but we've got an awful lot of work to do on that."
Gallo is optimistic. "I think there's great potential for products. Technologically it's difficult, but anything to strengthen our immune system by helping the healthy bacteria to survive is the way to go."
25th June, 2019