Scientists at John Hopkins University and Yale University have recently shown in mice that nerves specific to sensing “itchiness exist separately from nerves responsible for sensing pain. Up to that point, itchiness had been considered a byproduct of the nocioceptive pathway, especially after it was found that pain suppression using morphine led to chronic itchiness. However, Dr. Xinzhong Dong and his colleagues at John Hopkins isolated nerve cells in mice known to respond to itchy stimuli. When they rubbed the skin of these mice with capsaicin (the element in chili peppers that gives your tongue that painful burning sensation), the mice responded not by writhing in pain but by scratching, signifying that these cells only transmitted itch, not pain. Moreover, one of the itch-causing chemicals in this experiment was chloroquine, which has been notorious in malaria-treatment in Africa for causing itchiness. Because of the itchy side effects, many African patients refuse to take chloroquine.
The discovery of these itch-specific nerves is sparking more questions concerning the evolutionary benefits of itchiness. It’s a question that’s likely to have us all scratching our heads for a while. Full article can be found here