Armpits harbour a natural antibacterial agent.
Pongy pits hold a potent secret. Sweat contains a natural antibiotic, researchers have found, that may keep our natural skin-dwelling bugs in check.
Like a whiff of bad body odour, the protein Dermcidin clears the floor of disease causing micro-organisms. It sends bacteria E. coli, Staphylococus aureus and yeast Candidia albicans running for cover - and strikes them dead.
Birgit Schittek and her team at Eberhard-Karls-University in Tubingen, Germany came across Dermcidin while looking for proteins involved in skin cancer. Sweat glands constantly secrete the antibiotic, they found1. Excessive washing could remove our natural germicide.
Like deodorant, we need antimicrobials most when hot and sweaty. "Bacteria like warm, moist conditions," says Tomas Ganz who studies such 'antimicrobial peptides' at the University of California in Los Angeles. By limiting what lives on the skin, the protein may be "our first line of defence," he says. Sweaty people are not necessarily bereft of bugs, however: it depends how much Dermcidin they exude.
Antimicrobial peptides pepper all surfaces of the body that meet the outside - such as intestines, mouth and lungs, Ganz explains. Bacteria and peptides fight a constant battle, one evolving rapidly to cause infections, the other to thwart them.
How Dermcidin disables bacteria is a mystery. "It doesn't obey the rules," says Ganz. Other positively charged peptides punch holes in bacteria. Dermcidin is negatively charged, making this method unlikely.
When scientists work out the mechanism, they could use it to give skin an anti-bacterial boost, Schittek speculates: "One could put it into creams".
A square centimetre of greasy skin crawls with hundreds of thousands of microbes, says Keith Holland who studies skin flora at the University of Leeds, UK. Like those in the gut, these bugs play an important role, he thinks, keeping more harmful organisms at bay.
Skin crawls with hundreds of thousands of microbes Keith Holland University of Leeds, UK
Natural antibiotics in sweat may be particularly important when we damage the skin, he thinks, stopping resident bacteria getting inside to cause infection. Sweat's acidity and our rapidly sloughing skin may also keep surface-dwellers under control.
So while washing may be good for keeping friends, medicated deodorants and skin-washes which kill bugs could upset the skin's bacterial balance. "Leave well alone," Holland advises.
Schittek, B. et al. Dermcidin: a novel human antibiotic peptide secreted by sweat glands. Nature Immunology, advance online publication DOI: 10.1038/ni732 (2001).
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Dermcidin: a novel human antibiotic peptide secreted by sweat glands. Nature (2001). https://doi.org/10.1038/news011108-3