Hairy areas of a person’s body, especially the forearms and cheeks, remain as sensitive to touch as they age as they were decades ago.
- Sensitivity deteriorates in the hands, more specifically the index finger, with age.
- However, tactile sensing on the forearms and cheeks remains remarkably sensitive throughout life.
- According to French researchers, the preservation of tactile sensitivity is directly due to the presence of hair.
Like most primates, humans are sensitive to touch. When we are deprived of touch, we release more of the stress hormone cortisol, which causes a decrease in the immune system and an increase in heart rate and blood pressure. On the other hand, touch promotes the production of feel-good neurotransmitters, namely oxytocin, dopamine and serotonin.
Just like vision and hearing, our sense of touch is thought to deteriorate with age, “which contributes to the loss of manual dexterity and tactile function.” However, a new study, published in the journal Frontiers in Aging Neurosciencehas just revealed for the first time that the deterioration in touch sensitivity occurs only on areas of the body where the skin is hairless, but not on hairy body parts.
Index finger sensitivity to touch decreased with age
To reach this conclusion, researchers from the University of Aix-Marseille, the CNRS and the CRPN looked at how touch changes over the course of a lifetime, using different tests and on three parts of the body. As part of the work, the team recruited 96 left-handed women aged 20 to 75. They tested the sensitivity of their skin on the hairless tip of their right index finger, their right forearm and their right cheek, which are generally covered with a thin layer of hair. The participants were then asked to sit in a quiet room, close their eyes and wear noise-canceling headphones to avoid distractions.
In the first experiment, volunteers were asked to blindly move the tip of their right index finger across a series of 11 plates with differently spaced grooves, ranging from 3.6 mm to 6 mm wide. They were asked to indicate whether the grooves felt wider or narrower than those on a 4.8 mm wide reference plate. Each adult was tested 132 times and given a score for correct responses. The results confirmed that the index finger’s sensitivity for spatial exploration through touch declined with age.
The forearms and cheeks remain sensitive to touch throughout life
In a second, similar experiment, the scientists applied 13 types of monofilaments (each with a unique calibrated force ranging from 0.08 to 75 millinewtons) to women’s skin in a random pattern and with the dose gradually decreasing. Participants were asked to indicate each time they felt a touch. The experiment ended when one person made two errors in succession, indicating that they could no longer detect the stimulus accurately. “This is a widely used method for measuring touch sensitivity.”
“Force detection on the index finger also deteriorated significantly with age,” can be read in the results. In contrast, no changes were observed for tactile detection on the forearm or cheek. These data indicate that the cheeks remain exceptionally sensitive to touch throughout life. “This is a surprise, because hairless skin generally has a greater density of mechanoreceptors, which determine our sensitivity to touch, than hairy skin,” the authors said.
“Hair is our friend”
Researchers assume that the preservation of tactile sensitivity in the forearm and cheek is directly due to the presence of hair. “Hair is our friend. It protects us from bacteria, tells us the direction of the wind and transmits mechanical stimuli, even at very low forces. It is not for nothing that we have hair in the most sensitive areas,” has explained Jean-Marc Aimonettico-author of the research.
