Researchers have revealed that touch sensitivity may deteriorate with age on the glabrous skin of the fingertips, but not on the hairy skin of the forearm and cheek.
In the study, published in Frontiers in Aging Neuroscience, researchers from the Aix-Marseille University in France, provided new insights into how the sense of touch may change over the adult life span at different body sites.
They used calibrated monofilaments that delivered precise forces to measure the tactile detection thresholds on the right index finger pads, ventral forearms, and cheeks of 96 healthy female patients aged 20 to 75 years. Additionally, tactile spatial discrimination was tested on the participants' index fingers using plates with parallel ridges of varying distances.
The researchers demonstrated that both the tactile detection threshold and spatial discrimination ability on the index fingertip declined linearly with age. The tactile detection threshold increased from a mean of 2.4 mN (95% confidence interval [CI] = 1.1–3.6 mN) among the 10 youngest participants with a mean age of 22 years to 5.8 mN (95% CI = 1.5–10 mN) among the 10 oldest participants with a mean age of 72 years. The youngest participant with the lowest threshold (0.08 mN) and the oldest participant with the highest threshold (20 mN) were both 72 years old, highlighting the high variability in touch sensitivity among older individuals. Regression analyses indicated that the index finger tactile detection threshold increased by about 0.06 log units—corresponding to about a 15% increase in threshold force—per decade of age.
For the spatial discrimination test on the index finger, the minimum threshold was 0.16 mm for a 21-year-old, with the 10 youngest participants having a mean of 0.38 mm. The maximum threshold was 1.3 mm for a 70-year-old, with the 10 oldest participants averaging 0.62 mm. The spatial discrimination threshold increased by approximately 0.04 mm per decade.
However, no significant age-related changes in tactile detection were found on the forearm or cheek skin. The mean threshold for the forearm and cheek was a respective 4.7 mN and 0.9 mN for the 10 youngest participants and 5.6 mN and 1.1 mN for the 10 oldest participants. Notably, the cheek remained highly sensitive to touch stimuli throughout the life span, with many participants, regardless of age, achieving the lowest detectable force of 0.08 mN. The researchers suggested that an even lower threshold may have been found with a more sensitive test.
Further analyses revealed that the participants' performances on the fingertip detection and discrimination tests were positively correlated with each other. Tactile detection on the forearm was also associated with detection on both the finger and cheek. These findings indicated that although certain aspects of touch may decline with age, especially on the hands, there may also be individual differences in overall touch sensitivity across the body sites unrelated to aging.
The researchers proposed that intrinsic factors like skin thickness, receptor density, blood flow, and hair density likely played a role in the differences in touch sensitivity with age between the glabrous and hairy skin. Extrinsic factors such as use and wear-and-tear on the hands over a lifetime may also contribute to touch decline on the fingertips compared with more protected areas like the forearm. The high sensitivity on the cheek may be the result of its very dense concentration of thin hairs that help detect light touch.
The results of the study demonstrated site-specific changes in various aspects of touch perception with age, potentially offering insights into the mechanisms behind touch deterioration and maintenance as well as highlighting the need for more sensitive methods to evaluate tactile capacity—especially on hairy skin. A better understanding of touch sensitivity over the life span may aid in earlier detection of somatosensory disorders and guide strategies to help preserve this critical sense in older age.
The authors declared no competing interests.