Have you ever grabbed a hot pizza out of the oven and forgotten to use hand mitts? If not, have you ever stubbed your big toe on that coffee table leg or hit your knuckle against a steel beam underneath your car as you loosen a bolt?
In all three of these hypothetical scenarios, you would feel pain almost immediately. Some may react by using rather colorful vocabulary, but in every case, the instinct is to pull away from the source; to remove yourself from the cause of injury. In the case of the hot pizza pan, you might drop it on the floor! When you rammed your toe into the coffee table leg, you may have broken a few blood vessels and caused it to bruise. Likewise, you probably sliced some skin on that knuckle, and now it’s bleeding.
Pain isn’t pleasant, to say the least, but it is nevertheless a necessary occurrence when something in or on the body undergoes trauma. Put simply, pain is a sensation created by nerves sent to the brain. The brain in turn determines that something has been damaged, and thus a person will feel pain. Likewise, pain can serve as an identifier when something is awry. For instance, muscular aches may indicate a bodily infection such as the flu. A headache my occur as the result of something as simple as plugged sinuses or a very serious condition such as a cerebral hemorrhage.
On the other hand, a person can itch. To relieve this sensation, he or she will scratch the affected area on the skin. When someone has an allergic reaction, particularly on the surface of the skin, a substance called histamine is released and causes it to itch. At other times, scratching an itch can even be viewed as pleasurable. While it is normal to experience an itchy feeling anywhere from time to time, certain skin disorders can cause chronic itching, and scratching merely exacerbates the condition!
Until 1997, it was believed that itching was caused solely by lower levels of stimuli from the same nerves that result in the sensation of pain. However, during that year, researchers detected a family of nerves that respond to itch, but not pain. Further studies revealed that the sensations of itch and pain generated different activity in the frontal lobe of the brain.
Specifically, a biologist at Washington University in St. Louis named Zhou-Feng Chen, along with others, discovered a gene known as GRPR (gastrin-releasing peptide receptor) that caused mice to experience itchiness. Further experimentation revealed that when this gene was altered or deactivated, the mice stopped scratching when exposed to itching stimuli. However, the rodents still reacted to pain.
Although it has not yet been determined whether or not humans share the same sensory neurons, Chen’s research strongly suggests that there are two distinct pathways within the nervous system that interpret the sensations of pain and itching.
It has now been determined that itching and pain are not as closely related as once believed. An understanding of why is still the topic of speculation, but at this writing, research into this area of biology is ongoing.