Contagious itch in humans: a study of visual 'transmission' of itch in atopic dermatitis and healthy subjects

Abstract

Background: Anecdotal evidence suggests that 'contagious' itch occurs in daily life when we see other people itch and scratch. This phenomenon has not previously been studied systematically, and factors which can amplify itch perception were unknown.

Objectives: We investigated whether exposure to visual cues of itch can induce or intensify itch in healthy subjects and patients with atopic dermatitis (AD).

Methods: Participants received histamine or a saline control delivered to the forearm and were asked to watch short video clips of people scratching. Spontaneous scratching induced by visual cues was monitored and analysed.

Results: Patients with AD reported a higher itch intensity and scratched more frequently while watching itch videos, even in the presence of mock itch stimuli.

Conclusions: Human susceptibility to develop itch when exposed to visual cues is confirmed; it appears to be amplified in patients with AD. These findings suggest that interpersonal social cues can dramatically alter the subjective sensory experience of itch.

Figure 1

The perception of itch intensity increased significantly in atopic dermatitis subjects when they watched itch videos, in comparison to watching neutral videos, while the perception of itch increased just slightly in healthy volunteers. Visual Analog Scale ratings ± S.E.M.; visual analog ratings are expressed on a scale from 0 to 10. Saline = control delivered on the forearm; Neutral = neutral content videos.

Figure 2

Distribution and average duration of scratching episodes (in seconds ± S.E.M.) per extension area in AD and healthy subjects, exposed to itch and neutral videos in the presence of mock itch stimuli (0.9% aqueous saline). Localized episodes included scratching bouts limited to the same forearm where the local itch stimulus was applied; extended episodes included scratching motions extended beyond the same arm where itch stimulus was delivered and which exhibited a widespread distribution.

Figure 3

The distribution of scratching episodes in widespread (scattered) areas, in atopic dermatitis (AD) patients and healthy subjects, reveals that AD patients experienced an itch that extended beyond the local itch induction site, becoming generalized, while they watched itch videos (in red). Scratching beyond the local site in healthy participants was limited to the face, neck and the contralateral forearm (in blue). The areas scratched are shown in ranking order (by average duration) for an exposure to itch videos, when the local itch stimulus (histamine) was delivered to the right forearm (i.e. scratching on the contralateral forearm is represented). Atopic dermatitis subjects scratched mostly their contralateral forearm (1), mid-back region (2), face (3), neck (4) and scalp (5).{Note. Colored areas indicate in a figurative manner the location of scratching sites and are not intended to depict to scale the extension of the skin surface scratched}.

Figure 4

The average duration (in seconds ± S.E.M.) of extended versus localized scratching episodes in AD and healthy participants when a local itch stimulus (histamine) was paired with neutral and itch videos. Localized episodes included scratching bouts limited to the same forearm where the local itch stimulus was applied; extended episodes included scratching motions extended beyond the same arm where itch stimulus was delivered and which exhibited a widespread distribution.