Why scratching an itch feels so satisfying

An itch is a signal from nerve cells in the skin that something is irritating it. Scratching activates pain-sensing nerves whose signals temporarily suppress the itch. It can also release serotonin in the spinal cord, which dampens the itch and brings relief. But serotonin can also trigger itch-related nerve cells, explaining why relief is short-lived and the urge returns.