Contagious itch: what we know and what we would like to know

Abstract

All humans experience itch in the course of their life. Even a discussion on the topic of itch or seeing people scratch can evoke the desire to scratch. These events are coined “contagious itch” and are very common. We and others have shown that videos showing people scratching and pictures of affected skin or insects can induce itch in healthy persons and chronic itch patients. In our studies, patients with atopic dermatitis (AD) were more susceptible to visual itch cues than healthy. Also, personality traits like agreeableness and public self-consciousness were associated with induced scratching in skin patients, while neuroticism correlated with induced itch in healthy subjects. The underlying course of contagious itch is not yet fully understood. It is hypothesized that there are human mirror neurons that are active when we imitate actions and/or negative affect. Until now, there has been only limited data on the mechanisms of brain activation in contagious itch though. We have barely begun to understand the underlying physiological reactions and the triggering factors of this phenomenon. We summarize what we currently know about contagious itch and provide some suggestions what future research should focus on.

S2k Guidelines for the diagnosis and treatment of chronic pruritus – update – short version

“…Aprepitant may be considered in recalcitrant cases of CP. Both in individuals with healthy skin and patients with CP, pruritus and scratching can be elicited by mental and visual stimuli and by observing other people [ 39,40 ] . It has been shown that, compared to individuals with healthy skin, patients with AD react to the same stimuli with more pronounced pruritus and scratching [ 41 ] .…”

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

“…Papoiu et al, 2011;Schut et al, 2015a). Similar to pain, itch is a somatosensory sensation that can be a considerable burden for patients, especially when symptoms are chronic.…”

Functional magnetic resonance imaging in dermatology: The skin, the brain and the invisible

“…[104][105][106] Despite lacking clear evidence, [107] , it is speculated that in patients with delusional infestation, overactive contagious itch centres or an overactivity of the mirror neuron system may play a role. [98,108] Contagious itch points to the suggestibility of itch and potentially substantial placebo effects. [95] It has even been speculated that if there is a central source able to produce itch, there must also be a way to reverse the mechanism and produce cure.…”

“…[68] Interestingly, several brain regions linked to contagious itch are implicated in the simulation of actions, the so-called mirror neuron system, including the premotor cortex (BA6) and adjacent BA44. [97][98][99][100] This system is believed to be implicated in other archaic social contagious "resonance reactions" such as yawning (linked to BA 6 activity [101] ), laughing and the development of empathy. [102,103] Patients with autism, schizophrenia and psychopathy seem to have a mirror neuron system deficiency as measurable by an impaired ability of contagious yawning.…”