You (really) gotta scratch an itch 'til it hurts?

IT HAPPENS TO ALL OF US — beginning, perhaps, as a little tickle, hardly noticeable.

Maybe you're in an important meeting and you don't want to fidget. Or maybe your hands are full. So you try to ignore it, but the sensation grows -- an irritating, niggling feeling that gradually occupies more and more of your attention.

Finally, you can't take it any longer.

You have to scratch the itch.

Itching is as fundamental a sensation as pain and hunger, one we share with other creatures: "Every two-legged and four-legged animal itches and scratches," says Dr. Gil Yosipovitch, a dermatologist at Wake Forest University Baptist Medical Center in Winston-Salem, N.C. Yet for such a seemingly simple sensation, it's also surprisingly complicated.

Scientists have long wondered why pain -- for example, from scratching -- relieves an itch. They've searched for the nerves that send the itchy signal to the brain, and they've wondered what switches those nerves on and off.

And doctors and patients alike have wondered why the sensation can be so hard to expunge in those unfortunates who experience the extreme end of itching -- an itch that just won't go away.

Today, a small group of dermatologists and neuroscientists are starting to look at the biological mechanisms that lie behind itching. As they do so, they are finding curious overlaps between itching and that different-seeming sensation, pain. Though sometimes pain is itching's opposite, the latest findings are showing more and more similarities between the two.

And as they begin to understand the sensation's biology, dermatologists -- including ones at the world's only clinic dedicated entirely to the treatment of itch -- are developing new therapies for people who suffer the torment of chronically itchy hides.

An unbearable sensation

For most people, itching is only a mild annoyance, relieved by a quick scratch or maybe some skin cream. For others, the itch stays, stays -- and stays.

"It starts like any other itch, like you've been bitten or something," said David Hayes, a Los Angeles computer technician who has psoriasis, a noncontagious disease that causes skin inflammation, probably due to an overactive immune system. "But then it keeps on going. You've got to scratch it, and you've got to keep scratching until you're almost bleeding before it stops."

For people like Hayes with psoriasis, or for others with the skin allergy eczema, the sensation can be unbearable. "Itching is the worst thing," says Susan Lipworth of Bloomfield Hills, Mich., who has had eczema for 13 years. "It never stops -- it never stops -- it wears you down."

Lipworth, who is also a board member of the National Eczema Assn., a patient advocacy group, says that scratching becomes so automatic, she even does it while sleeping. "I'm waking my husband up with my scratching," she says.

An estimated 4.5 million adult Americans have psoriasis and 9 million have eczema, according to the American Academy of Dermatology, most tolerating long-term itch that doesn't go away with scratching. Burn patients, and people with certain kinds of nerve damage, also often have severe itching -- as can people with liver and kidney diseases and some who are infected with HIV, due to the infection itself and the medicines they must take.

Such itches can erode a person's mental health, experts now say.

Many studies have found that people with severe itching from psoriasis, eczema and kidney dialysis are more likely to be depressed than others. In a 1998 study published in the British Journal of Dermatology, for example, researchers from the University of Western Ontario in Canada reported that almost 10% of 217 patients with psoriasis had had suicidal thoughts.

For many people, the itchiness also prevents them from sleeping. In a study in 2002, Yosipovitch found that 84% of 102 eczema patients had trouble falling asleep due to itching.

Lack of sleep is a particular problem in children with eczema. (The condition affects more children than adults.) A 1995 study, conducted at the Maelor Hospital in Wrexham, United Kingdom, estimated that preschoolers with eczema lost an average of two hours of sleep per night, and that the deficit led to behavioral problems at school.

Rebecca Litke, a professor at Cal State Northridge, has a 12-year-old daughter with eczema. "My daughter, for the first eight years rarely slept through the night," she says. That meant that Litke rarely did, either. "It has been awful," she said. "For years you're functioning on three or four hours a night."

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