An itch (Latin: pruritus) is a sensation felt on an area of skin that makes a person or animal want to scratch it. It is a distressing symptom that can cause discomfort. Scratching may cause breaks in the skin that may result in infection.
Pruritus can be related to anything from dry skin to undiagnosed cancer.
The central chemical in itch is histamine, a molecule released by mast cells in the skin. Histamine is the chemical that causes the itch and reddening when bitten by insects. It binds to local nerve endings on specific receptors.
Itch from cutaneous (skin-related) stimuli, such as movement of small hairs on the body, is transmitted along the same pathway as pain. Itch caused by histamine is transmitted to the brain by a different neural pathway, described in 2001 by Andrew et al. As with pain, histamine-induced itch travels via the spinothalamic tract, but in fibres specific for itch.