Placebo and nocebo effects on itch: effects, mechanisms, and predictors.

Placebo and nocebo effects have been extensively studied in the field of pain and more recently also on itch. In accordance with placebo research on pain, expectancy learning via verbal suggestion or conditioning has shown to induce placebo and nocebo effects on itch, in which the combination of both procedures seems most promising. Moreover, itch can also be transferred 'contagiously' in which suggestion and social behavioural learning seem to play a role. With regard to predictors of placebo and nocebo responding on itch and contagious itch, preliminary evidence suggests a role for individual psychological characteristics and personality traits regarding negative outcome expectancies. Although findings on placebo and nocebo effects on itch seem comparable to pain, we have only just begun to understand the underlying mechanisms and predictors of placebo and nocebo effects on itch.