Itch
A itch is a sensation felt on an area of skin that makes a person or animal want to scratch it. The feeling of itchiness can be caused by movement of hairs, or release of a chemical (histamine) from cells under the skin. Itchiness is regarded as protective, as it helps creatures remove parasites that land on them.Itch from cutaneous (on the skin) 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. Histamine is the chemical that causes the itch and reddening when bitten by insects. As with pain, histamine-induced itch travels via the spinothalamic tract, but in fibres specific for itch.