Interpersonal stroking touch is targeted to C tactile afferent activation.

C tactile fibers are a specialized group of fibers innervating the non-glabrous skin that are tuned to light gentle stroking applied with velocities between 1 and 10 cm/s. Those fibers add to the sensation of interpersonal caressing and pleasant touch. It is unclear whether people spontaneously apply touch that is tuned to optimally activate those fibers. This was investigated in three studies. In study one, 45 participants (21.8 ± 2.3 years, 24 women) were asked to stroke an artificial arm. In study two, 32 participants (28.3 ± 8.7 years, 16 women) were asked to stroke their partner. In study three, 11 parents (29.4 ± 5.7 years, 6 women) were asked to stroke their babies. Stroking velocity was tracked in all conditions. Stroking velocities were significantly slower in the partner touch and baby touch condition than in the artificial arm condition and all of the participants stroking their partner or baby used velocities that can activate C tactile fibers. We conclude that human social stroking is optimized for C tactile stimulation.