The pleasurability of scratching an itch: a psychophysical and topographical assessment.

BACKGROUND: Scratching an itch is perceived as being pleasurable. However, an analysis of topographical variations in itch intensity, the effectiveness of scratching to provide itch relief and the associated pleasurability has not been performed at different body sites. OBJECTIVES: To examine the role of scratching pleasurability in providing itch relief by investigating whether itch intensity is perceived differently at three different sites and to assess a potential correlation between the pleasurability and itch attenuation induced by scratching. METHODS: Itch was induced on the forearm, ankle and back using cowhage spicules in 18 healthy subjects. These sites were subsequently scratched by an investigator with a cytology brush immediately following itch induction. The intensity of itch with and without scratching at these sites and the pleasurability of scratching were recorded by taking visual analogue scale ratings at 30-s intervals. RESULTS: Mean itch intensity and scratching pleasurability ratings at the ankle and back were significantly higher than on the forearm. For the forearm and ankle, the greater the itch while scratching, the higher was the pleasurability. A higher baseline itch was linked to a higher itch reduction secondary to scratching in all tested areas. Pleasurability paralleled the curve of itch reduction for the back and forearm; however, scratching pleasurability at the ankle remained elevated and only slightly decreased while itch was diminishing. CONCLUSIONS: There are topographical differences in itch intensity, the effectiveness of scratching in relieving itch and the associated pleasurability. Experimental itch induced by cowhage was more intensely perceived at the ankle, while scratching attenuated itch most effectively on the back.

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

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.

Ethnic differences in pain, itch and thermal detection in response to topical capsaicin: African Americans display a notably limited hyperalgesia and neurogenic inflammation.

BACKGROUND: Topical application of capsaicin commonly produces burning, stinging and itching as well as hyperalgesia to heat stimuli via activation of transient receptor potential vanilloid subtype 1. OBJECTIVES: To investigate whether there are differences in sensory response and neurogenic inflammation to topical capsaicin in four different ethnic populations with different skin types. METHODS: The study was performed in 40 healthy subjects consisting of 10 African Americans, 10 East Asians, 10 Hispanics and 10 Caucasians. Warmth sensation and heat pain detection thresholds, as well as pain intensity, were measured before and after application of capsaicin or placebo on forearms along with skin blood flow and the extent of the flare reaction. RESULTS: In African Americans the heat pain detection threshold, pain intensity and skin blood flow did not change significantly after capsaicin application, while in the other three ethnic groups a significant change occurred characterized by hyperalgesia and vasodilatation. The postcapsaicin warmth sensation threshold increased in African Americans and decreased in Hispanics, the latter also uniquely experiencing postcapsaicin itch. CONCLUSIONS: Our observations indicate that African Americans display a limited hypersensitivity following topical capsaicin, compared with the three other ethnic groups.

Itch characteristics in atopic dermatitis: results of a web-based questionnaire.

BACKGROUND: Itch significantly impairs the quality of life of patients with atopic dermatitis. However, only a few previous studies have examined the specific characteristics of itch in atopic dermatitis. OBJECTIVE: To examine the frequency, intensity and perceived characteristics of pruritus among individuals with atopic dermatitis. METHODS: Questionnaire reliability and validity were established in pilot testing. Survey participants completed the comprehensive, web-based 'Characteristics of itch' questionnaire. Participants provided anonymous demographic information and answered questions regarding itch intensity, frequency, timing, duration, location, associated symptoms and itch descriptors. RESULTS: A total of 304 individuals with atopic dermatitis completed the web-based questionnaire. Itch occurred at least once daily in 91% of the individuals surveyed. Of the 32 itch descriptors rated by survey participants, 31 demonstrated a statistically significant positive correlation with the participants' ratings of itch intensity (P < 0.001). More than half the survey participants reported pain (59%) and heat sensation (53%) associated with itch. CONCLUSION: The questionnaire was found to be a useful tool in characterization of itch. Pain appears to be an important component of atopic dermatitis. The strong correlation between itch descriptors and itch intensity suggests that such descriptors serve as strong indicators of the symptomatology in atopic dermatitis.