Few things are as satisfying as scratching an itch – and now scientists have scratched the most nagging of all: why do we itch?

For the first time, experts at Harvard Medical School have identified how a common skin bacterium makes us itch by acting directly on our nerve cells.

Researchers exposed the skin of mice to the staphylococcus aureus bacterium, and found they developed an intensifying itch over several days.

Not only was this down to the bacterium itself, but because it made the rodents hypersensitive to light touches that would normally not cause an itch.

This response is common in patients with conditions like eczema, but it can also happen in people without any underlying conditions – think of those itchy Christmas jumpers you’ll be wearing next month.

Multiple modified versions of staphylococcus aureus were engineered, some lacking specific pieces of its usual molecular makeup, to identify a single bacterial enzyme responsible for initiating an itch.

This enzyme, dubbed V8, triggers an itch by activating a protein called PAR1. It’s found on skin neurons that carry various signals – like pain, heat, and itch – to the brain.

Scratching the itch

When researchers repeated the experiments in lab dishes containing human neurons, they also responded to V8.

This was true regardless of whether there were cells implicated in skin allergies or allergic reactions.

Study author Liwen Deng said: “We show these things can be decoupled. You don’t necessarily have to have inflammation for the microbe to cause itch, but that the itch exacerbates inflammation on the skin.”

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With PAR1 identified as the chief cause of an itch, researchers set about how to block it.

Given it’s a protein also involved in blood-clotting, they tried an already approved anti-clotting drug – and it worked.

Itchy mice experienced rapid improvement when treated, both in terms of itches and any skin damage.

Researchers believe it could be used as an anti-itch medication for humans, becoming the basis of new creams.

Dr Deng said: “Itch can be quite debilitating in patients who suffer from chronic skin conditions.

“Many of these patients carry on their skin the very microbe we’ve now shown for the first time can induce itch.”

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