This article is part of a special issue investigating key questions about skincare. Find the full series here.
Look under the microscope at any square centimetre of human skin and you will find it teeming with bacteria, fungi, mites and viruses. It might sound yucky, but your skin鈥檚 microbiome is an important defence against invading pathogens.
鈥淏ecause there are all these bacteria already there, it鈥檚 quite hard for a pathogen to get a foothold,鈥� says , a dermatologist at the University of Manchester, UK, and chief science officer of AxisBiotix, a company that offers skincare products based on microbiome research. 鈥淏acteria can also wage warfare on each other by secreting different chemicals that inhibit the growth of pathogens.鈥�
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Trained immunity
The skin microbiome, together with the gut microbiome, also helps train our immune system during childhood, teaching it to attack pathogens and ignore harmless stimuli. This could explain why people who have a greater diversity of skin bacteria are less .
Beneficial skin bacteria could also be the key to maintaining . Our skin is like a fortress constructed from layers of skin cells packed together. In between the cells are lipids that keep the skin supple and plump, and certain bacterial species help to replenish those stores.
鈥�Cutibacterium stimulates the skin to produce sebum, which protects the skin, reduces water loss and increases hydration,鈥� says , who studies wound healing at the University of Hull, UK. Staphylococcus epidermidis and Streptococcus thermophilus can produce ceramides, meanwhile, which can also reduce water loss and protect the skin barrier.
Skin probiotics
As we age, the delicate balance of the skin microbiome can be disrupted, as the 鈥済ood鈥� bacteria that protect us from infection and keep our skin hydrated are replaced by harmful, pathogenic species. This state of skin 鈥渄ysbiosis鈥� has been linked to acne, rosacea, psoriasis and eczema, as well as problems with wound repair.
Given these benefits, it should be no surprise that scientists are looking for ways to keep our skin鈥檚 allies happy. One idea is to use prebiotics, or nutrients that feed and encourage the growth of good bacteria.
People who have a greater diversity of skin bacteria are less likely to have allergies
These include inulin, a dietary fibre found in asparagus and bananas, which can be eaten to support gut health or applied topically to the skin. In addition, scientists are exploring whether slathering live good bacteria such as S. thermophilus, together known as probiotics, directly on the skin could allow them to become established there.
Making a working probiotic is easier said than done, however. 鈥淚t鈥檚 technically extremely challenging just to keep the bacteria alive,鈥� says Bernhard Paetzold, co-founder and chief scientific officer of , a company that aims to treat conditions by restoring the skin鈥檚 microbiome.
The third idea, known as postbiotics, involves applying the products of beneficial bacteria to the skin as a supplement. Some researchers advocate for using sphingomyelinase, an that boosts production of ceramides, as such a treatment.
Ongoing human clinical trials are testing the effects of prebiotics, probiotics and postbiotics on . 鈥淭heir initial findings are certainly promising, but we need larger-scale studies to provide convincing evidence for their wider use,鈥� says Wilkinson.
There may be other means of tending your skin microbiome. Gardening has been to increase the diversity of bacteria on the skin, albeit temporarily: most new microbes fail to take root and disappear after just 12 hours.
Gut-skin axis
Another option could be to receive mud therapy at a spa. A of five previous studies concluded that, in many cases, natural muds were effective at wiping out pathogenic strains of bacteria while leaving beneficial ones unharmed. It is important to note, however, that many of the studies weren鈥檛 conducted in humans.
You may have too frequently can disrupt the skin microbiome, but the , so there may be no need to forgo your cleansing routine on account of your resident bacteria.
Perhaps the easiest way to boost your skin microbiome is to eat healthily (see What should we be eating to give us better, healthier skin). We now know that the bacteria in your gut can influence your skin health through what is known as the . This might explain why diets high in unhealthy foods, like fast food, may trigger acne, while eating lots of fibre can of eczema, at least in mice. 鈥淎s ever, a healthy diet with fresh whole foods is always the answer,鈥� says O鈥橬eill.
