Epidermal microstructure and tactile sensitivity in the glabrous skin of hands and feet
Glabrous skin on the human palms and soles is specialised for mechanical interaction and is characterised by papillary ridges, an absence of hair follicles, and a thick stratum corneum. While gross morphological differences, such as the increased thickness of the plantar stratum corneum, are well-documented, the fine-scale structural features associated with individual ridges and whether they help explain differences in tactile perception remain poorly understood. Here, we employed optical coherence tomography, automated image segmentation, and 3D reconstruction to generate high-resolution models of the stratum corneum and viable epidermis across six sites on the hand and foot for 27 participants. Our morphological analysis revealed that while the stratum corneum was thicker on the foot sole than the hand, the thickness of the viable epidermis remained remarkably consistent across all sites. Furthermore, papillary ridge width increased in a distal-to-proximal fashion and was larger on the foot. We also found that internal ridge architecture was considerably more pronounced than the topography observable on the skin surface. Correlating these structural parameters with psychophysical measures, specifically absolute force and two-point discrimination thresholds, demonstrated distinct drivers for tactile sensitivity. Force thresholds were primarily governed by a combination of skin thickness and innervation density, and additionally on the foot by papillary ridge width and internal ridge depth. In contrast, spatial acuity was best predicted by innervation and papillary ridge width. These findings provide a precise quantification of glabrous skin morphology and offer new insights into the process of mechanotransduction by highlighting how tissue architecture might contribute to human tactile perception.