The relation between human hair follicle density and touch perception

Abstract

Unmyelinated low threshold C-tactile fibers moderate pleasant aspects of touch. These fibers respond optimally to stroking stimulation of the skin with slow velocities (1–10 cm/s). Low threshold mechanoreceptors are arranged around hair follicles in rodent skin. If valid also in humans, hair follicle density (HFD) may relate to the perceived pleasantness of stroking tactile stimulation. We conducted two studies that examined the relation between HFD and affective touch perception in humans. In total, 138 healthy volunteers were stroked on the forearm and rated the pleasantness and intensity. Stimulation was performed by a robotic tactile stimulator delivering C-tactile optimal (1, 3, 10 cm/s) and non-optimal (0.1, 0.3, 30 cm/s) stroking velocities. Additionally, a measure of discriminative touch was applied in study 2. HFD of the same forearm was determined using the Cyanoacrylate Skin Stripping Method (CSSM), which we validated in a pretest. Women had higher HFD than men, which was explained by body size and weight. Furthermore, women rated affective touch stimuli as more pleasant and had higher tactile acuity. Depilation did not affect touch perception. A weak relationship was found between the C-tactile specific aspects of affective touch perception and HFD, and the hypothesis of HFD relating to pleasant aspects of stroking only received weak support.

Assessment of experimental orofacial pain, pleasantness and unpleasantness via standardized psychophysical testing

“…A large overlap was seen between modalities and intensities inducing pain and unpleasantness (Price, ) with no stimuli consistently perceived as unpleasant but not painful. There was no significant difference in pleasantness scores between stroking velocities; however, they did follow an inverted U ‐shape profile peaking at 1–3 cm/s, complement findings from studies from the forearm (Ackerley, Carlsson, et al, ; Jönsson et al, ; Loken et al, ; Luong et al, ).…”

MAGHair: A Wearable System to Create Unique Tactile Feedback by Stimulating Only the Body Hair

“…Body Hair: We hypothesise that the different body hair characteristics of the different participants had an overall impact on the perceived sensation. Previous research in affective touch already explored some of these relations between hair type and the perception [12]. During this experiment, we required participants to have enough hair on their arms, which limited our selection of participants to males.…”

“…Body Hair: In MAGHair, we elaborated on three different recipes and applied one of them to the forearm of different users. However, different users had a different type of hairs with different characteristics, such as density and length, which are likely to generate a different haptic sensation [12]. We encourage future research to focus on developing similar recipes and applying them to different types of body hair, such as the scalp hair, eyebrows, forearm, etc.…”

Itchy body: Topographical difference of itch and scratching and C Nerve fibres

“…Of note, CT afferents are found only in the hairy skin and hardly seen in the glabrous skin such as the palms. Interestingly, one report demonstrated that women had higher hair follicle density than men, and women rated affective touch stimuli as more pleasant and had higher tactile acuity . However, we cannot assess the innervation density of CT afferents due to lack of proper methods and we currently do not know whether CT afferents have functional difference among different parts of the body.…”