Many people complain about ‘moving itches’, but I had never noticed it before. So, I waited for an itch. Surely enough, one came along almost straight away and I diligently scratched it. It moved.
At first, this might seem like the power of suggestion – perhaps I felt it because I was told it would happen? But make no mistake, moving itches are very real.
Something irritates our skin, making it itch. When we feel the itch, we scratch it. It’s very satisfying, but our skin isn’t quite so keen on it. Scratching an itch damages the skin and causes pain. Not a lot, I’ll grant you, but enough that our brain doesn’t like it. It responds by releasing a chemical known as serotonin to make us feel better. Also called ‘the feel good hormone’, it makes us feel happy. It also turns out that serotonin itself also makes us itch.
Researchers have found that mice with no serotonin scratch their itches less. When these mice are given serotonin, they scratch more. This is because there are some ‘itch signal’ nerves in our spinal cord that have both ‘itch receptors’ (the GRP receptor) and ‘serotonin receptors’ (the 5-HT1A receptor) on them. When serotonin binds to the 5-HT1A receptors on these nerves, ‘the itch signal’ is sent out to our brain, making us feel an itch. This surge in serotonin makes us itch more, either in the same place as before or somewhere else.
It’s likely that the ‘moved’ itch was already there but was too minor for us to notice. When serotonin gets involved, the itch gets itchier and so we scratch it. Which releases more serotonin, making us itch even more. It’s a vicious cycle that’s pretty hard to break.
So, next time you feel an itch, maybe you should just try to ignore it. Which, as I am discovering, is easier said than done.
Answer by Kate Timms
Zhao, Zhong-Qiu, et al. (2014). Descending Control of Itch Transmission by the Serotonergic System via 5-HT1A-Facilitated GRP-GRPR Signaling. Neuron, 84(4), 821-834