ABSTRACT
Although the sensations of itch and pain are quite distinct and result in different behavioral responses (i.e., scratching versus withdrawal), they share multiple important features. In human skin, both sensations can be produced by stimuli of the same modality (e.g., mechanical, thermal, chemical, and electrical), with stimuli at low intensities producing itch and, at higher intensities, inducing the sensation of pain (von Frey 1922; Lewis et al. 1927; Bishop 1943). Itch or pain can furthermore be induced from apparently identical spots in human skin (von Frey 1922; Bishop 1943), and loss of itch sensation is paralleled by the loss of pain sensitivity (Török 1907; Thöle 1912; von Frey 1922; Bickford 1938; McMurray 1950; Nolano et al. 2000).
