Why do we instinctively touch the painful areas of our body? Research shows that touch can reduce pain, and also offers explanations for this phenomenon.
A sore in the mouth, a scratch on the leg, or a painful pimple—we’re all experienced the urge to repeatedly touch them. Why do we touch specifically in the painful areas? Researchers offer several possible explanations.
The first, and perhaps most intuitive, is that we want to feel and assess the extent of the damage caused by the injury and understand how much it hurts. But are there other factors at play?
One possible reason is that touch activates mechanoreceptors, which are touch receptors in the skin. These receptors transmit sensory information to a part of the brain known as the somatosensory cortex, responsible for processing sensory information from the skin, including texture, temperature and pain. When these receptors report a sensation of pain, activating them through touch of the affected area likely provides some relief from the pain. A study on anesthetized laboratory animals demonstrated that certain nerve cells in the spinal cord have a broad spectrum of action: they respond to touch in a specific manner, while responding differently to pain. Other nerve cells are more specific, responding exclusively to a stimulation of touch or pain. The nerve cells with a broad spectrum of action underlie the phenomenon of pain relief through touch.
Certain nerve cells in the spinal cord have a broad spectrum of action, responding to touch in a specific manner and to pain in a different manner. Illustration of the pain sensation pathway, from the skin or muscle to the brain | Witt-Deguillaume, BSIP, Science Photo Library
Pain Relief Through Additional Stimuli
One of the studies on this topic examined the response of mice when they simultaneously experience both heat-induced pain and touch in the facial region. Researchers divided the mice into two groups: mice with intact whiskers and mice whose whiskers had been trimmed. Subsequently, they induced pain in the facial area of all the mice while touching the whiskers of the mice in the first group. The researchers followed the “grooming” movements made by the mice, in an attempt to remove the painful stimulus, which reflected the intensity of the experienced pain or discomfort. Mice with trimmed whiskers, who received only a painful stimulus without touch, engaged in more “grooming” movements on their faces, indicating that they experienced greater discomfort. The researchers concluded that certain nerve cells, which play a role in encoding pain information, respond differently when mice experience both pain and touch on their faces, compared to a situation where they only experienced pain.A video showing a mouse responding to stimuli:
The researchers also investigated the impact of “switching-off” some of the nerve cells in the somatosensory cortex, the brain region mentioned earlier. They found that “turning off” these nerve cells cancels the positive effect of facial touch and whisker movement on the sensation of pain. This underscores the involvement of this brain region in pain relief through touch.
Touch helps to reduce pain in humans as well. In a 2010 study, researchers asked the research participants to place their index finger and thumb in hot water and their middle finger in cold water (try this at home, but not with boiling water, of course!). This situation creates an illusion that the middle finger is “burning”, and indeed, the participants reported a sensation of pain. When the participants were asked to touch the sore middle finger using the fingers of the other hand, more than half of them reported a reduction in the sensation of pain.
The level of pain is not determined solely by the pain signals reaching the brain, but also by the way the brain interprets these signals. Illustration of the somatosensory cortex | Kateryna Kon, Science Photo Library
Pain Reflected in the Mirror
Studies show that not only touch, but also visual perception of the painful body part has an impact on pain perception. In one study the researchers used a mirror that distorted the size (but not the shape) of the reflected image. They induced a painful stimulus on the participants’ palms while participants saw their palm reflected in a mirror at a size that was either equal to, larger than or smaller than its actual size. Observing their palm in the mirror at the time of the painful stimulus helped the participants cope with the pain, compared to a situation in which they were shown something else instead. Moreover, the size of the palm as reflected in the mirror influenced the perception of pain. Participants who saw their palm reflected at an enlarged size reported less pain compared to those who saw their palm reflected in its actual size or smaller.
In summary, the level of pain is determined not only by the pain signals reaching the brain, but also by the way the brain interprets these signals and links them to the representation of the entire body. Touching the painful body part, and to some extent, even looking at it, sends additional information and signals to the brain, helping the brain create a more comprehensive understanding of the body parts and the signals received from them, ultimately putting the pain into perspective and reducing the perception of pain.
Massage and Hygiene
Touching the painful part of the body can have additional benefits - massage can increase the blood flow to the injured area, facilitating local metabolism and aiding in faster recovery. No less importantly, touch can also provide psychological comfort by fostering a connection with the body and by giving us a sense of control over the situation. It's important to note that in the case of open wounds, touching can lead to infection. Therefore, open wounds should be properly cleaned, disinfected and dressed rather than just touched. In other cases, there is no harm in touching the area that hurts, it may even provide relief.