Stop Scratching (November 4, 2014)
It makes the itch worse. Just like gramma said. (Here’s where she gets her own back, after having been wrong about coffee being bad for you last week.)
What happens is that scratching is mildly painful and since the spinal column can’t carry every sensation that is input into it at once, signals going up the pain nerves push some of the itch nerve (called GRPR neurons) signals out of the way and the brain senses less itching. (That is how rubbing makes something hurt less too, incidentally; the vibration signals from rubbing an injured body part block some of the pain signals.)
The pain signals from scratching cause brain release of serotonin, which is its standard procedure in response to pain. However, and this is the tricky part, that same serotonin also increases the intensity of the itch signals travelling along the GRPR neurons. So you get into an endless loop here of scratching feeling good but making the itching worse. You just can’t win.
What IS itching, anyway? Itching is a sensation that causes the desire to scratch. Aren't you glad you asked? (That is straight out of Wikipedia, and honestly, it’s the best definition I found for it. Don’t worry when your doctor looks things up on Wikipedia, like half of us do. Worry when he or she DOESN’T look things up on Wikipedia.) Itching is similar in nature to pain, and the two different nerves are physically very close to each other in the spinal cord as well.
It's speculated that itching evolved as a signal to remove insects, because interestingly pain makes you withdraw from the stimulus, but the closely related sensation of itching makes you reach for it. Anyway, if something is really itching and driving you nuts, you quickly reach a point where scratching isn't helping, and although we know why that happens, our new knowledge isn't providing any new solutions. Rather than progressing to digging a dinner fork into the itchy area, then, try applying heat or cold and see if that does it.
--dr. diane holmes
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