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Updated: May 30, 2026

Cheek Injection Model for Simultaneous Measurement of Pain and Itch-related Behaviors
Published on: September 27, 2019
Anatomy and neurophysiology of pruritus
Akihiko Ikoma1, Ferda Cevikbas, Cordula Kempkes
1Department of Dermatology and Surgery, University of California, San Francisco, San Francisco, CA, USA. IkomaA@derm.ucsf.edu
Abstract:
Itch has been described for many years as an unpleasant sensation that evokes the urgent desire to scratch. Studies of the neurobiology, neurophysiology, and cellular biology of itch have gradually been clarifying the mechanism of itch both peripherally and centrally. The discussion has been focused on which nerves and neuroreceptors play major roles in itch induction. The "intensity theory" hypothesizes that signal transduction on the same nerves leads to either pain (high intensity) or itch (low intensity), depending on the signal intensity. The "labeled-line coding theory" hypothesizes the complete separation of pain and itch pathways. Itch sensitization must also be considered in discussions of itch. This review highlights anatomical and functional properties of itch pathways and their relation to understanding itch perception and pruritic diseases.
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