At the moment we’re born, each of us is seeded with trillions of bacteria cells that live and thrive on our skin. These cells form what’s known as our skin microbiome. The exact makeup of each person’s microbiome is as unique as a fingerprint and as we go through life meeting new people, interacting with environments, adopting different lifestyles, and changing with age, so too does the diversity and health of this microbiome.
Something as simple as leaving the house can cause our skin microbiome to adapt. As can living with someone, to the extent where two people’s microbiomes become so intertwined that algorithms can correctly identify cohabiting couples based on their microbiomes alone.
“The skin microbiome is a natural ecosystem of bacteria that live on the skin,” explains cosmetic doctor and skin specialist Dr Martin Kinsella. “It works to guard the skin against harmful pathogens to the point where a well-functioning skin microbiome is the foundation of a healthy immune system.”
As the microbiota colonise our skin, they flourish by feeding on the salt, water and oil (sebum) we produce naturally. This keeps our ecosystem in a delicate balance. When a pathogen comes into contact with a flourishing microbiome, it’s prevented from colonising the skin by being crowded out. Our microbiome produces antimicrobial compounds and nutrients that act as a form of protection.
If our skin is the first line of defence against pathogens and injury, then our microbiome is its armour.
Indicative of this protective nature, studies have found links between babies born via caesarean section, meaning they don’t come into contact with vaginal microbes during birth, and increased instances of allergies and asthma later in life. Unicef has made skin-to-skin contact a key component of its birthing standards, citing the practice’s power to “enable colonisation of the baby’s skin with the mother’s friendly bacteria, thus providing protection against infection.”
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When this protection is weakened by damage, or by the presence of harmful bacteria, the microbiome’s delicate balance can be thrown off kilter. This imbalance has been linked to dry skin, eczema, acne and psoriasis and, according to the Skin Microbiome in Healthy Ageing (SMiHA) network, some 50 per cent of the UK population suffer a microbiome-associated skin complaint each year.
“The chemicals in skincare products can disrupt the natural microbiome of the skin's delicate balance of oil and bacteria,” says Kinsella. “Antibacterial agents are a big factor in this, and other products with harsh chemicals that alter the skin’s natural pH balance.”
This was seen during COVID-19 when a study found that “changes to microbial flora” caused by the increased use of sanitiser was linked to an increase in skin damage. Medications and antibiotics have been shown to destroy the beneficial bacteria on the skin, leaving it more prone to infections. Conditions such as acne and dandruff can also be a sign of an imbalanced skin microbiome.
Once unbalanced, the microbiome can’t as effectively protect against further bad bacteria, and a vicious cycle occurs. With eczema, bad bacteria causes the skin to become inflamed, patients scratch their skin therefore damaging it further, which lets more bad bacteria in.
Kate Porter, founder of skincare brand Harborist explains further: “More severe eczema and dry skin has been associated with an abundance of a bacteria known as Staphylococcus aureus. There is evidence that reducing S. aureus, to restore a more diverse microbiome population, reduces symptoms of eczema. But it’s a chicken and egg situation. Does the imbalanced microbiome cause these issues or vice versa?”
As we age our microbiome then goes through further shifts. This shift is not only associated with visible changes – wrinkles, dark spots, dry skin – but with internal changes, too. There is one school of thought that as our microbiome changes with age, our skin’s ability to protect us from UV radiation decreases. Thus increasing our susceptibility to skin cancer.
Recent studies have even shown the skin microbiome to be a more accurate predictor of chronological age compared to gut. With this theory, a person’s microbiome could, hypothetically at least, be used to assess life expectancy. “Ageing has a profound effect on the skin microflora in terms of both species and numbers,” explains the team leading the SMiHA. “Therefore, human skin presents an excellent system to establish how changes in the microbiome influence biological age.”
That’s not to say microbiomes are the sole cause of such conditions and diseases – genetics and lifestyle play significant roles, for instance – but disruption to our skin’s ecosystem is a contributing factor. Modern hygiene habits, including daily showers, are believed to play a role. Harsh skincare products are often blamed. Researchers from Finland found a correlation between an increasing prevalence of allergies and atopic conditions and the decline of biodiversity in urban areas.
Yet just as everyday products have been linked with disrupting the microbiome, an increasing number of brands are now releasing products infused with prebiotics, probiotics and postbiotics to balance this disruption.
While probiotics refer to ‘friendly’ bacteria, and prebiotics are nutrients that feed these probiotics, postbiotics are what’s left behind in the process. The jury is still out on the benefits of topical probiotic and prebiotic skincare, largely due to the infancy of the research and the fact the use of live bacteria in cosmetics is a regulator sticking point, but postbiotics in skin products are already commonplace.
Lactic acid, for instance, found in off-the-shelf skincare, is a by-product of the fermentation of a probiotic called Lactobacillus. When applied topically, it has been shown to hydrate, reduce the signs of ageing and calm redness.
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Researchers are also looking into the possibility of microbiota transplants to solve skin problems. In one study published in 2018 in the journal JCI Insight, an abundance of S. aureus in the microbiomes of people with atopic dermatitis was replaced with a bacteria known as Roseomonas mucosa “with significant decreases in measures of disease severity, and topical steroid requirement”.
The issue with almost all of these findings, however, is that the underlying mechanisms of the skin microbiome remain largely unknown, and its impact is disputed. For all the studies linking C-section births with lower immunity, there are studies that either fail to find the same correlations, or find associations that are statistically irrelevant.
“When the skin is healthy, we believe the skin microbiome is healthy too, however we don’t know this for sure,” says the SMiHA team. “Our understanding of how to manipulate the skin microbiome using everyday products is still very poor.”
“As consumers we like to be able to link a specific ingredient in our skincare with a specific outcome, but there are multiple factors influencing our microbiome,” Porter adds. “It’s tricky to change it for the better using just one thing because the microbiome varies so much between people. There’s also no single best direction to shift it.”
Recently, initiatives such as the Skin Trust Club have started collecting samples from the public to delve deeper into our skin health and its inner workings. From a biomedical standpoint, researchers are also exploring the effects of antibiotics on the skin microbiome, to see if we can drive down antimicrobial resistance.
This is far easier said than done, though.
“There is a huge commercial pull to explore how to improve skin through a microbiome-targeted approach,” concludes the SMiHA team. “However, separating the effects of topical products on the microbial population and the skin cells – in a way that allows us to be able to categorically say microbial targeting drives healthier skin – is a tough challenge for the scientific community.”
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