The relationships between skin hardness, pressure perception and two-point discrimination in the fingertip

With the recent introduction of computer-assisted sensibility testing devices, it is possible to investigate the hypothesis that the neurological mechanisms responsible for perception of pressure and two-point discrimination are influenced by skin hardness. This study examined the relationships between the skin hardness of the human index and little finger pulp and the perception of pressure in 25 adults. Skin hardness was measured using the Derma-Durometer. Pressure perception was measured with the Pressure-Specified Sensory Device for both static and moving touch stimuli and for two-point discrimination. The mean hardness of the fingertip pulp was 12.5 +/- 0.6 gm/mm2. There was no statistically significant difference in hardness between the dominant and non-dominant, right and left, index and little, or male and female fingertips. Skin hardness was independent of age for this population. The highest correlation, which was r = 0.46, was found between the cutaneous pressure threshold for one-point static touch and skin hardness. While this degree of correlation is significant at the P < 0.02 level, the r2 = 21%, demonstrating that this degree of correlation leaves 79% of the variability unexplained. These results suggest a physical interaction between mechanoreceptors and dermis that is only partially explained by the hardness of the skin.