Itching Skin

Everyone itches, many different times in many different places, sometimes all over all at once. Unfortunately, for such a common condition (it's called pruritus in medicalese) doctors aren't exactly sure what's going on. Or why scratching feels so good. It's a mystery, as maddening as a mosquito bite in the middle of your back.

For ages, doctors and scientists thought itches traveled the same neural pathway as pain. That theory has changed in the past decade. Now it's known that itching has its own special pathway. The sensation of itching is transmitted by tiny C fiber nerves (the body's smallest) that extend nearly to the skin's surface.

These C-fibers can be activated directly by an irritant that gets into your skin (through cracks), or indirectly by immune-system cells that patrol the skin and release histamine when they detect something foreign (such as mosquito spit). The histamine binds to the nerve endings, which send a message to the brain that the skin needs attention.

And that's the essential difference between the brain's reaction to the twin sensations of pain and itching: Pain causes a withdrawal response; itching causes a response that makes you want to go toward the site of the itching.

So why does scratching work, at least temporarily? One reason may be that the brain can process only one signal of sensation at a time from a particular location in the skin, and by providing another type of irritation, we can suppress the itch.

Also scratching generates heat and if you heat up the nerves that cause itching, you can suppress it. Which leaves the issue of why scratching feels so good? If you follow the human urge to scratch, you're going along a well-trodden neurological pathway that is hard wired into the brain. It's very satisfying.

Medicines or tricks that suppress itching are sometimes not as gratifying. That shudder of pleasure may be from a release of endorphins that give you a natural high.

Too much scratching, however, can trigger an "itch-scratch cycle," in which the scratching aggravates the body into releasing more histamine, which causes swelling, which stimulates nerve endings, which causes more itching...

You need to break the cycle. We'll show you how, particularly with some classic itches. First, some all-purpose tricks.

• Ice it. Cold tends to make the C-fibers sluggish.
• Fool it. Scratch the corresponding spot on the opposite limb. Nerves on one side of the body run up the other side of the spine, and somehow it tricks the brain.
• Ignore it. Playa game on your Sony PSP to distract your brain. A recent Australian study found that allowing kids to playa virtual-reality video game while they were being treated for bums resulted in reduced pain and itching. It makes more sense to understand and attack the source of the itch than to battle it once it has arrived.