Scientists have only just begun to scratch the surface of the mystery of why we itch. For example, Medical Daily recently reported on a recent study that explained part of why itching is contagious. However, why does only our skin become itchy? Is itchiness a form of pain? Why does just reading about itchiness make you itchy? A recent study published in Nature Neuroscience sought to answer two of those three questions.
Previous studies on itchiness had found that some pain nerves fire in response to itchy stimulants. Those findings, along with an inability to actually find nerves that responded solely to itchiness, prompted researchers to believe that pain and itch were processed by the same nerve fibers and were simply interpreted by the brain differently. However, according to Live Science, that explanation seemed imperfect to Xinzhong Dong and his team of researchers at Johns Hopkins University. For example, when a person is bitten by a mosquito, he or she tends to hone in on the sensation, attempting to scratch the itch. On the other hand, if a person feels pain after coming into contact with a hot surface, like an iron, the instinct is to back away.
In order to find a more conclusive answer, Dong and his team genetically engineered mice so that their nerve cells would glow fluorescent green when they were firing. Then the researchers exposed the mice to irritating substances, like histamines or the active ingredient in itch powder. They found that, when the nerve cells burned out, the mice became less itchy.
However, that finding in and of itself did not settle the matter, because the mice could still conceivably feel pain, so in a second experiment, researchers activated just the itch-detecting nerves in the mice's faces. The mice reacted by scratching their faces with their hind legs, indicating itchiness, while scratching their faces with their front paws would have indicated pain.
The study also revealed that itch nerves sit in the spine by the cord and only are activated in the skin. That finding explains why individuals do not typically feel itchy internal organs.
The findings mean that scientists may be better able to create anti-itch medications. The ones currently on the market typically work by reducing inflammation or targeting a narrow set of causes, like hives. However, a treatment that targets the nerve cells directly may be an improvement over these therapies.