Asked by: Luke Spalding, Birmingham
Studies using functional magnetic resonance imaging (fMRI) have shown that scratching causes patterns of brain activity that are associated with pleasure and reward. This effect is strongest when you do the scratching yourself and when you are actually scratching an itch, rather than just an arbitrary patch of skin. But contrary to what you might expect, or might have read elsewhere, there’s no clear evidence that this pleasure comes from a release of endorphins – it happens purely in your brain and spine.
This mechanism may have evolved to encourage us to dislodge skin parasites. All the evidence suggests that it’s a very ancient response, because all vertebrates scratch themselves – even fish!