Various models of itch induction and their relationship to pain sensitivity

Pruritus, a complex multidimensional sensation accompanying diverse dermatological and systemic disorders, affects a substantial global population. Nevertheless, the pathophysiological mechanisms underlying chronic pruritus remain incompletely understood. Standardized experimental paradigms for inducing pruritus are essential for establishing a foundational understanding of chronic pruritus. This study aimed to develop a standardized laboratory protocol for pruritus induction, investigate the relationships between sensitivities to different pruritus modalities, and explore the associations of pruritus sensitivities with pain sensitivity and other somatosensory sensitivities, thereby exploring the potential neural mechanisms. This work recruited 124 healthy participants and employed three validated pruritus induction paradigms: mechanical stimulation via calibrated feather brushing, chemical stimulation via epicutaneous application of 1% histamine dihydrochloride solution, and electrically evoked pruritus using high-frequency, low-intensity transcutaneous electrical nerve stimulation. Concurrent Quantitative Somatosensory Testing assessed subjective itch intensity and its correlation with other somatosensory profiles. All three paradigms effectively evoked significant pruritic sensations. Critically, no statistically significant differences were observed in subjective intensity ratings across the induction methods. Correlational analysis revealed significant positive associations between intensities evoked by feather brushing and histamine application, and between feather brushing and electrical stimulation. However, no significant correlation was found between histamine-evoked and electrically evoked itch intensities. This dissociation suggests both shared and distinct neural substrates mediate processing of different pruritus modalities. Furthermore, the study identified complex interactions between pruritus and other somatosensory modalities. Feather-evoked mechanical itch intensity demonstrated a significant negative correlation with mechanical pain thresholds. Similarly, histamine-evoked chemical itch intensity showed a significant negative correlation with heat pain threshold as well as heat pain tolerance thresholds. This work establishes a rigorous methodological foundation for future mechanistic research into pruritus and facilitates the development of targeted therapeutic strategies. The established paradigm in this study can serve as a core tool for objectively assessing an individual's itch sensitivity, deepen the understanding of itch perception, and act as an objective indicator for evaluating the progression of chronic itch disorders and the efficacy of their treatment in clinical practice.