Chances are, as you're reading this, you've got an itch. (And if you don't now, you soon will.) It could be anywhere. Your chin, your scalp--your left elbow. Without thinking much about it, you reach out and (\o7 ahhh!\f7 ) scratch it.

How fitting that one of life's most common irritants should be paired with one of its greatest satisfactions.

But while itching is a universal experience, doctors know precious little about it. While that may not seem like a big deal, it has great significance for the thousands who suffer from intractable pruritus (the $50-office-visit term for itching). For them, scratching brings no relief and probably makes matters worse. Medication, likewise, may be of little help; sufferers have few choices but to endure the maddening sensation.

That may soon change, thanks to research into the mechanism of itching and the development of more effective treatments. These studies also shed new light on the way nervous and immune systems interact.

Researchers have difficulty agreeing on exactly what constitutes an itch. There's no synonym for the word, usually defined as an irritating sensation that provokes the urge to scratch.

Some scientists hold that itching is a minor form of pain. They say the sensation is transmitted to the brain via the same neural pathways taken by pain signals.

Others, such as Dr. George Murphy, a dermatology and pathology professor at the University of Pennsylvania, believe itching, while related to pain, is in a class by itself.

"It's clearly a very separate physiological phenomenon," he says. "Our understanding of the physiology and pathology of it is embarrassingly rudimentary." Murphy notes that while people can easily feel pain inside their mouths, they seldom if ever experience itching there.

In a recent article in the journal Nature, Murphy and his research colleagues detailed their findings about a type of nerve fiber embedded in the skin that is found in close proximity to two types of immune cells, one of which is known to play a role in itching.

The team also found that nerve fibers release special proteins called neuropeptides that stimulate the immune cells and, in turn, release chemicals that can lead to itching and other reactions.

"This has led us to believe there's a very intimate interplay between the nervous system and the immune system," Murphy says. "Conventional Western medicine and dermatology has not paid a tremendous amount of attention to the mind-body connection with respect to skin disease."