Scratching an itch causes the brain to release the mood-regulating and pain-controlling neurotransmitter serotonin, according to new research from Washington University School of Medicine in St. Louis, MO. The researchers suggest that serotonin has the effect of intensifying the itch sensation.
Serotonin has a muddling effect on the sensation of pain and itch, whereby, as serotonin spreads from brain to spinal cord, pain-sensing neurons instead influence itch intensity.
Scientists know from previous studies that a mild amount of pain in the skin is caused by scratching, which temporarily interferes with the itching sensation. This interference happens because, while scratching, nerve cells in the spinal cord carry pain signals to the brain instead of itch signals.