You know that prickly feeling you get under a woollen jumper, or when someone lightly brushes your skin? Heck – right now, somewhere on your body, you’ve probably even got an itch caused by nothing in particular. Well, scientists at Harvard Medical School in the USA have discovered its cause: a (very gross) bacteria living in your skin.
And (as if it couldn’t get worse) the researchers have found this happens because the bacteria, known as Staphylococcus aureus, literally changes your nerve cells. If your skin wasn’t crawling before, we bet it is now.
But how does it make you itch? Published in the journal Cell, a new paper reveals that the pesky little microbe releases a chemical which activates a protein in our nerves. This sends a signal from our skin to our brains – which our brain perceives as an itch.
If it makes you feel any better, there are plenty of good bacteria that also live in your skin. In fact, this amazing organ is kept healthy by a fine balance of microorganisms that call your skin their home.
But it’s when this finely balanced microbiome becomes out of whack that S. aureus can go rampant.
The researchers discovered this through research on mice and human cells. To start, they exposed the skin of mice to S. aureus. The mice developed increasingly intense itches – directly due to the bacteria, but also in response to stimuli that shouldn’t be so irritating, like a light touch.
Next, the scientists isolated a single enzyme that they knew the microbe releases upon skin contact. They tested just this enzyme on the mice and measured levels of this enzyme in different human patients’ skin. The scientists' conclusion: this enzyme is the single-handed culprit behind the itch.
In fact, patients with dermatitis have higher levels of this enzyme, known as protease V8, than people with healthy skin.
Proteaste V8 activates a protein in our nerves called PAR1, which usually lies dormant but awakens when the V8 ‘snips’ one end of it. The researchers tested V8 in lab dishes containing human neurons, and found these also responded to the enzyme.
Scratching the surface of itch research
The discovery explains why people with eczema and atopic dermatitis itch a lot.
If you’ve had a bad itch, you know how good it feels to scratch it – but you’ll probably also know that it usually makes things worse. Itching, especially for those with skin conditions, can actually cause skin damage and even pain, the researchers warn.
That’s why they’re hoping that their findings will improve medicines and creams designed to treat itching linked to imbalances in the skin microbiome (like dermatitis and psoriasis).
How? The researchers knew that PAR1 (the protein that the microbes activate) is involved in blood-clotting, so they tried an approved anticlotting drug to treat the itching – and it worked. The rate of itching and resulting skin damage lowered in the mice.
What remains unclear is why the bacteria would want to make our skin crawl, evolutionarily speaking.
“It’s a speculation at this point, but the itch-scratch cycle could benefit the microbes and enable their spread to distant body sites and to uninfected hosts,” said first author Dr Liwen Deng.
“Why do we itch and scratch? Does it help us, or does it help the microbe? That’s something that we could follow up on in the future.”
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