Effect of scratching and friction on human skin in vivo

To investigate effect of scratching and friction on human skin function and functional differences between scratching and friction.

Forty healthy volunteers were enrolled. Scratching and friction behavior was modeled by scalpel and sandpaper simulation to forearm for 80 times, respectively. Noninvasive bioengineering devices were used to measure basic skin physiological parameters and exfoliated stratum corneum collected and protein quantified. Parameters were recorded at baseline (BL) and after every 20 times interventions (20, 40, 60, and 80 times).

Compared to BL, transepidermal water loss (TEWL) value increased significantly at both scratched and friction sites (P < .001) with a significant higher value for friction (P < .001). There was no significant difference in stratum corneum hydration (SCH) value postscratching (P > .05), while it decreased first and then increased significantly at friction site (P < .001). Roughness values (contract (CONT), variety (VAR), and scaliness (SEsc)) were raised significantly at both sites (P < .001). Net change in CONT and SEsc values of friction was higher than scratched sites (P > .05). There was no significant difference in blood flow after both scratching and friction (P > .05). Quantity of keratinocyte protein from friction sites was statistically higher than scratching after 80 times interventions (P < .05).

Both noninvasive detections and protein quantification indicated more damage from friction, which may have significance for behavior guidance of patients with pruritus and implication for further investigation.