Itching Is Its Own Sensation, Not Just Pain's Little Cousin

By Allison Bond | August 7, 2009 12:04 pm

itchy mouseScientists seem to have finally put to rest a longstanding debate over itchiness: Is the urge to itch a sensation that is simply another interpretation of pain, or a separate feeling altogether? It turns out the two stem from different cells and neural pathways, according to a new study in Science.

To find out whether pain and itchiness are separate sensations, scientists injected mice with a neurotoxin. This toxin homed in on and killed cells that contained active versions of GRPR, a gene that is involved in the sensation of itchiness. (The same research group discovered this itch gene in 2007.) Afterward, the mice could no longer respond to any itchy stimuli. They didn’t flinch. They made no effort to scratch. But they did respond to pain just like other mice do [TIME], showing that the gene needed to be active to transmit itchiness, but not pain. It’s just one study, but it provides strong evidence that itchiness and pain are processed by separate neural pathways.

There are two general causes of itchiness. One, caused by bug bites or allergic reactions, is linked to the presence of the chemical histamine. But most chronic, severe itching is not linked to the chemical – and does not respond to standard anti-histamine treatment [BBC]. This second source of itchiness can be particularly irritating; because its cause can be mysterious, it’s therefore often difficult to remedy.

The results of the study could help scientists develop ways to combat persistent itchiness by aiming specifically for the pathways involved in the urge to itch. The findings held for all types of itch-causing substances, including those that release histamine (think bug bites and allergic reactions that can be treated with Benadryl) and other agents responsible for chronic, severe itching not eased by antihistamines [LiveScience]. Still, some experts caution that although the findings are important, other research suggests that the pathway studied is not the only one that causes people to itch. Lead author Zhou-Feng Chen said he has many more questions, such as how the GRPR neuron passes information to the brain and what other itch-specific genes the neuron contains [LiveScience].

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Image courtesy of Science/AAAS

CATEGORIZED UNDER: Health & Medicine, Mind & Brain
MORE ABOUT: family health, senses
  • NewEnglandBob

    What is the reason for itching? Most of the time the bug bite itch comes too late to do anything about it, so the urge to scratch can be more harmful than helpful. Allergic reactions would probably be better off having the pain reaction and there also, scratching is rarely helpful.

    As far as the ‘other’ type of itches, I have has a spot on my back that itches very often (over countless years)and there is no bug bite, no allergic reaction and nothing there. Scratch the itch and it gives temporary relief but a few minutes later it is itching again. Here also, the scratching is not helpful, so again I ask, what is this pathway there for?

  • spha-odon

    Human Ill Controlled
    Willpower As Restraint

    When itches of the ivy overcome the power of your will,
    You really want to dig it, scratch it, rub it till
    The bumps are raw and weeping and they begin to ooze
    Because it feels so good your fingernails to use.

    Just remember scabs will come and cover up the “gnaw,”
    The skin that you’ve scratched so raw,
    But time and healing will take longer
    As poison ivy itches will grow stronger.

    If your willpower is of no use
    In overcoming skin abuse,
    The time it takes to heal
    Will only add to how you feel.

    When your human will proves weak,
    Restraints you’ll need to seek
    To curb and quell the hurt you cause
    The prior irritations from abusive paws.

    There is a principle that seems here to arise
    That should help both of us to realize
    That to gain control of human ill
    One must exercise the power of his own will.

  • http://n/a Elaine Rydman

    this was a great article for someone who has been suffering for months like me and explains why the prednizone isn’t helping.. thank you.


  • guard card california

    Your blog is laid out well. pleasing theme, helpful content. Thanks for the hard work!


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