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    What's an Itch?

    By Joanne Barker
    WebMD Feature
    Reviewed by Louise Chang, MD

    Does the world outside make you itch? Warmer months can bring you in contact with any number of scratchy culprits: poison ivy, bug bites, and sunburn, to name a few.

    From a survival perspective, there isn’t a good explanation for why we itch. One theory goes that animals itch in order to get parasites off their skin, and our desire to scratch an itch could be a carryover from that instinct.

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    Another possible explanation is that pain and itch engage many of the same areas of the brain. When you scratch an itch, you cause yourself enough pain to relive the itch, temporarily. Regardless, itches are best left unscratched.

    Find out what happens to your skin when you develop an itch.

    Never Too Old for Poison Ivy

    “I’ve had patients in their late 70s come in with their first case of poison ivy,” says Lisa A. Garner, MD, FAAD, clinical professor of dermatology at the University of Texas Southwestern Medical School. “People think if they’ve never had poison ivy, they never will,” she says. But that’s not the case. The CDC estimates that 80% to 90% of adults are allergic to urushiol, the oil in poison ivy -- and poison oak and poison sumac -- that causes the reaction.

    It is true that you can come in contact with poison ivy and not develop a rash the first time. Below the surface, however, your immune system could be arming itself for the next exposure. The next time you are exposed to urushiol, you’re likely to have a reaction.

    Some, but not all people, may see their sensitivity to poison ivy decline as they get older, Garner says.

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