The secret to clear skin may lie in the cocktail of strains of a common bacterium that lives on your skin.
Propionibacterium acnes bacteria are abundant in the pores on everyone's face. They have been implicated as a cause of pimples, but why they aggravate spottiness in some people but not others has been a mystery.
The discovery that there are "good" and "bad" types of P. acnes offers a clue. It also opens up the possibility of developing treatments customised to the flora of an individual's skin.
The condition affects 85 per cent of teenagers and 11 per cent of adults, and as anyone with acne can testify, existing treatments such as antibiotics have limited effectiveness and can make skin dry out or cause redness and peeling.
A team led by Huiying Li of the University of California, Los Angeles, has analysed bacteria from the nose skin of 49 people with acne and 52 controls. "Not all P. acnes strains were created equal," says Li.
Of the thousands of P. acnes strains the researchers identified, the most common 66 were investigated in depth by completely sequencing their genomes. Of these, 63 strains were found in people with and without acne, but two appeared to be linked to acne, and one to healthy skin.
One of the "bad" strains was uniquely found on spotty skin; the other was also found in 16 per cent of samples from people without acne. The "good" strain was hardly found in people with acne but was present in a fifth of those with clear skin.
Uniquely, the "bad" strains had extra groups of genes derived from viruses. These rogue genes can potentially aggravate acne and include one which binds the bugs unusually tightly to human cells. Because spots are caused by our immune system going into overdrive in response to the presence of P. acnes, resulting in inflammation, this "tightness" gene "means it can trigger a stronger immune response", says Li.
The "good" strain, meanwhile, lacked these genes. Instead, it had genetic components enabling it to recognise and destroy the rogue genes, which means it doesn't cause the skin to become inflamed and spots don't erupt.
Since not all the individuals with clear skin had the "good" strains and not all with acne had the "bad" ones, other factors – such as the tendency of the immune system to over-react or an individual's genetic make-up – might dictate whether good or bad strains grow on skin. In other words, the experiment does not demonstrate what came first – the bad strains of bacteria or the acne, a point raised by researchers not involved in the work.
"Whether the strains are cause or effect is not addressed by this study," says Martin Blaser of New York University. "Nevertheless, this is an important first step in understanding the role of P. acnes in disease."
Probiotics for acne
Li says further investigations are under way in the same people to find out how the balance of good, bad and neutral strains changes over time. She is hopeful that it might be possible to develop creams customised to each person's unique cocktail of skin bacteria to prevent or treat acne.
"Good strains might be used as probiotics to stop skin blemishes before they start, much like yogurt contains good strains of bacteria to fight off bad bugs in the gut," she says.
Another possibility might be drugs that kill only the bad strains. At present, acne is treated with antibiotics that kill all bacteria on the skin, including harmless ones that helpfully prevent nasty strains from taking hold. Exclusively killing the bad strains would be more beneficial, says Li.
Journal reference: Journal of Investigative Dermatology, doi.org/kng
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