ABSTRACT
In 1660, Hafenreffer defined itch as "unpleasant sensation eliciting the urge to scratch"-a definition that still holds true today from a clinical point of view (1). Whereas the peripheral pathways of the neural signaling of itch were the subject of many recent and older studies, not much is known about the central nervous, supraspinal processing of itch, and the corresponding scratch response (2--4). The itch receptor, a subpopulation of chemosensitive unmyelinated C-fibers, has been identified (5-7). There is evidence for spinal gating of the sensation (8,9). Emotional modulation of the perception of itch is also well known (10-14) and results in marked inter-and intraindividual variations. Thus, there is a need for an objective measurement of itch as it has been established in pain research (8,15-19). Results ofour previous studies on objective covariates of itch using axon reflex correlations (20) and a new multidimensional itch questionnaire (10,11) suggest the existence of several components of itch perception. Itch is a multidimensional experience. Moreover, a prominent influence of psychological and cerebral factors on skin inflammation has been suggested, but the mechanisms are unclear (4,13, 14,21).
