Scientists have shown scratching helps relieve an itch by blocking activity in spinal cord nerve cells that transmit the sensation to the brain. However, the effect only seems to occur when an itch is actually present -- scratching at other times makes no difference.
A new study on primates shows that scratching the skin blocks activity of nerve cells in the spinothalamic tract during itchiness, preventing the spinal cord from transmitting signals from the scratched area of skin to the brain.
This information could eventually lead to ways to relieve chronic itch effectively for the first time. However, more information is likely still needed about the chemistry underpinning the effect.