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Itchy skin, itchy eyes, and itchy rashes can drive anyone to distraction, and chronic itch is a common problem.
What kinds of conditions cause chronic itching? An itch that just won't quit is a common complication of eczema. Chronic itch is a frequent result of allergies, kidney disease, and diabetic neuropathy. People who use opioid drugs like Vicodin or Oxycontin, whether by prescription or illicitly, often have to deal with itchy skin. All of these conditions are becoming more and more common, especially opioid abuse. About one in five people has to deal with a condition causing chronic itching at some point in life, and common medications don't do a very good job of providing itch relief.
What's Wrong With Anti-Itch Medications?
There are some causes of itching that medicine can control fairly well. Allergic itching is relatively easy to stop because it is the result of misdirected activity of the immune system. Turn off the production of histamine with an antihistamine, and the itching stops. Medication for allergic itch usually works.
Other kinds of itching aren't as easily controlled by medication. Part of the treatment for eczema involves restoring moisture to the skin, but choosing the wrong moisturizer can make itching worse. Itching caused by neuropathy can only be treated by restoring nerve function (until recently, old-style antidepressants called MAOI inhibitors might have been used for this purpose), and itching that results from opioid use and abuse is only responsive to discontinuation of the opioid medication. For most of us, the best remedy for an itch is to scratch.
Why Does Scratching Relieve Itching?
It seems a little odd that we humans are put together in ways that make the infliction of pain and tissue injury, by scratching ourselves with our fingernails, as the way to stop the sensation of an itch. The reason scratching itches works has to do with the way our nervous system transmits sensations from the skin.
The sensory nervous system doesn't consist just of long neurons connecting the skin to the spinal cord. There are also smaller structures called interneurons. Sometimes interneurons amplify a nerve signal. Sometimes they stop it from being transmitted at all. The painful sensation of scratching stops the sensation of an itch because the interneurons block scratching signals. To the brain, it is more important to be informed if there is skin injury than it is to be informed of an itch.
The problem with scratching is that it injures the skin, and the process of healing the skin creates even more itching. However, painful scratching isn't the only way to stop the sensation of itching.
- Pressure sensations also override the sensation of itch. Placing steady pressure on itchy skin will stop the itching.
- Cold or cool sensations make contact with a kind of interneuron that can also override the sensation of an itch. A cold compress may be exactly what is needed to stop itching skin.
- Certain chemicals also activate interneurons that stop itching sensations. Menthol, for instance, soothes an itch, as does neem. Capsaicin (the chemical in hot peppers) also stops itching, but with the sensation of burning.