Why Scratching Just Makes You Itchier

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You know that scratching at a mosquito bite only makes the itch worse, but why? Isn’t the whole point of a scratch to cancel out an itch? (Also, why is writing these sentences making me all itchy?) Some new research published today in the journal Neuron provides some answers. 

First, here’s how the itch-and-scratch combo works: A scratch relieves an itch by producing a brief, small sensation of pain, which kind of distracts the brain from the itchiness. “The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain,” lead researcher Zhou-Feng Chen explained in the press release. "But as serotonin spreads from the brain into the spinal cord, we found the chemical can ‘jump the tracks,’ moving from pain-sensing neurons to nerve cells that influence itch intensity."

To study this, Chen and colleagues began by genetically engineering a group of mice so that they did not have the genes necessary to make serotonin. The researchers then injected the mice with a substance that causes itchiness and found that these mice didn’t scratch as much as normal ones. But when the Frankenmice were given a serotonin injection and then given the itchy injection, they scratched as much as their non-genetically engineered mouse-peers.

Yes, it’s a study in mice, and you are not a mouse; still, the researchers expect the results to apply to humans too. It’s a vicious, itchy circle.