Itch, to most, is a common nuisance, although when chronic it can negatively affect quality of life. It is obvious that itch is processed differently than pain, but how it differs is not clear. Researchers have been trying to find a path that specifically mediates itch. They have found that itch is mediated through at least two different pathways: histamine dependent and histamine independent. However, many of the mediators involved in the transduction of itch also mediate pain. Although some itch-specific neurons have been found, the majority of the pruritogenic neurons are also responsive to pain stimuli. Two theories that can explain how the brain processes itch and pain as different sensations are the specificity theory and the selectivity theory.
Rappaport, N. (2016). Itch Mediation and How It Differs from Pain. The Science Journal of the Lander College of Arts and Sciences, 9 (2). Retrieved from http://touroscholar.touro.edu/cgi/viewcontent.cgi?article=1046&context=sjlcas