Tough itch to scratch - Macleans.ca

Tough itch to scratch

The science of skin problems is often better explained by a neurologist than a dermatologist

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Tough itch to scratchDigging up her garden one spring, Christine Jackson broke out in a “crazy itchy” rash. It spread from one leg to the other, then across her entire body. “Soon I was covered head to toe with this rash that made me scratch so much at night, I was bloody,” says Jackson, who lives in Ottawa. Prescription creams didn’t help; oral medication just made her groggy. Her doctor and dermatologist were baffled. Still, the itching didn’t stop. “You can’t focus, you can’t think. All you’re trying to do is not scratch, because once you do, the itch just gets worse,” says Jackson, who has scars from scratching so hard. “It is completely crazy-making.”

Today, Jackson is executive director of the non-profit Canadian Skin Patient Alliance. “At some point,” she says, “everyone in this country will have a skin disease or condition.” Indeed, they may be more common than many people realize. Last year, Maclean’s and Scienta Health published a test in this magazine and online to help readers identify symptoms. Skin and hair problems were the second-most frequently cited; of those, dry, itchy skin, acne, rashes, hives and redness were the biggest complaints. While itchy skin affects virtually everybody at some point, researchers are only now beginning to understand how we itch, and why.

Itching is probably the least understood sensation in the human body, says Glenn Giesler, a professor of neuroscience at the University of Minnesota. Some itches arise from histamine reactions to plants or bugs, and “are generally easy to treat,” he says. Topical steroid creams are used against eczema and psoriasis. The most “clinically interesting” forms of itch, though, often can’t be helped: those caused by AIDS, Hodgkin’s disease, or kidney failure, all of which can bring on furious bouts of itching. “Most people who complain of itching go see the dermatologist, but they only study skin,” says Zhou-Feng Chen, an investigator at the Washington University Pain Center. The study of itching is better suited to neuroscientists, he says, “because it affects your brain.”

While itching was long regarded as a less intense form of pain, it’s not so. Our reflex reaction to both is different: if your hand approaches a pain source (say, a fire), you automatically pull back. But if your hand begins to itch, “you use a finger to scratch it,” says Chen, who was the first to identify a gene responsible for itching. What’s more, one cancels the other out. “You negate the itch with the pain of scratching,” Giesler says. Other painful stimuli have also been shown to reduce itch: for example, “injecting the active ingredient in hot peppers” into the site, or applying a very hot towel. Pain and itching, it seems, have an inverse relationship. “Morphine reduces pain, but if you take too much, you get itchy,” says Giesler.

Why does scratching help? It seems to short-circuit itch signals as they travel up the spinal cord to the brain. In an experiment with lab monkeys, Giesler (with student Steve Davidson) attached electrodes to their spinal nerves. After injecting the monkeys with an itch-inducing chemical and then scratching the site, they noticed the itch signal was temporarily shut down. Scratching might provide relief from more than just itch: in a separate study, a team from Wake Forest University Baptist Medical Center found that parts of the brain associated with unpleasant emotions and memories are less active during scratching.

But itching doesn’t require a physical cause. As anyone who’s ever blushed with embarrassment can attest, emotion affects the skin, too. “Stress is a natural reaction to prepare us for fight or flight,” says Petra Arck of McMaster University, who holds a Canada Research Chair in neuroimmunology. “In a fight, your skin must be prepared to be damaged.” According to her work, stress causes new nerves to sprout in the skin, pushing disease-fighting cells to its surface. But too much stress inflames the skin, leading to the dreaded itch. A mother’s stress can even impact her baby: Arck has found that children of women who felt stress during pregnancy were more likely to suffer from eczema.

Even contemplating itching can be enough to bring it on (the very act of reading this article may have left readers scratching themselves). Researchers have succeeded in making subjects feel itchy just by showing them pictures of fleas, mites and scratch marks on the skin. “Itching definitely has a psychological aspect,” Chen says. “Nobody really knows why.”

Skin treatments work some of the time; and sometimes, nothing works. Dr. Elaine Chin, co-founder and chief medical officer of the Scienta Health Group, suggests an inappropriate diet (including a lack of vitamins E and C, or good fatty acids found in fish; or even a food intolerance) could be a factor. “Itch is not a trivial problem,” Giesler says. “We’re beginning to understand how it works, so maybe someday we can treat it.”

As for Jackson, her rash remains undiagnosed (the dermatologist concluded it might be a form of eczema). After several months of treatment, it went away—although it still flares up now and then, mostly in times of stress. How does she cope? “I have a big, big vat of heavy-duty cortisone,” she says.

Skin dos & don’ts

DO:

  • Use mild detergents to wash clothing, with no bleach or fabric softener
  • Double-rinse clothing
  • Moisturize often, especially in colder weather
  • Choose cotton for bed linens and clothing
  • Reduce stress as much as possible

DON’T:

  • Expose skin to very hot or very cold weather
  • Expose skin to excessive heat or low humidty
  • Dress in synthetic fabrics or wear wool next to skin
  • Use harsh detergents or perfumed products

SOURCE: Canadian Dermatology Association