Now, there is evidence that capsaicin -- the substance that gives cayenne, jalapenos and other hot peppers their fiery sting -- relieves pain.

Pepper cream -- in a highly purified form -- was introduced in 1987 to treat the severe and chronic pain associated with shingles. But researchers are discovering more uses for it all the time.

So far, studies suggest capsaicin reduces pain associated with arthritis, diabetes, muscle and joint problems, phantom limbs and cluster headaches. More research is underway to see if capsaicin eases mouth pain in cancer patients and alleviates chronic nasal stuffiness of people who don't have allergies.

The latest evidence -- a study done at the Mayo Clinic in Rochester, Minn. -- suggests capsaicin (pronounced cap-SAY-a-sin) reduces pain from post-surgical scars.

In the Mayo study, Dr. Charles Loprinizi found a pepper cream called Zostrix-HP was three times more effective than placebos in relieving pain. Zostrix is an over-the-counter topical cream made by Genderm, a Chicago pharmaceutical company.

For the study, 99 patients who had long-standing postsurgical pain received eight weeks of treatment with pepper cream and eight weeks of treatment with an identical-looking placebo cream. The creams were applied four times a day.

Although the pepper cream caused significantly more skin-burning, redness and coughing than did the placebo, patients using it experienced significantly more pain relief, Loprinizi reported.

The average pain reduction for patients using the capsaicin was 53 percent, compared to 17 percent with the placebo. About 10 percent of the patients reported complete pain relief.

But just how is it that the stuff in a chile pepper quells pain?

The idea may sound illogical, but herbalists have known for centuries that chile peppers relieve pain.

Michael Castleman reports in his book, ``The Healing Herbs -- The Ultimate Guide to the Curative Powers of Nature's Medicines'' (Bantam Books, $6.99), that 17th-century English herbalist Nicholas Culpeper promoted red peppers, used sparingly, to aid digestion, relieve toothaches, comfort a ``cold'' stomach and expel kidney stones. In the United States, after the Civil War, physicians called red pepper capsicum and recommended using it externally for arthritis and muscle soreness, Castleman writes.

It wasn't until the 1980s that scientists tested capsaicin's effectiveness in clinical trials and began to understand how it works.

Ken Verburg, a pharmacologist and vice president of product development for Genderm, says capsaicin works by acting like a key. It unlocks the receptors on nerve cells and reduces the production of ``substance P,'' a chemical that causes pain. With less substance P, the brain receives fewer pain messages.

It also has the added benefit of acting only to relieve pain and not creating other problems like numbness. Applied repeatedly to the skin, capsaicin eventually causes the nerve cells to use up their substance P, so pain stops. But if patients stop using capsaicin, substance P builds up again and pain returns.

Highly potent, capsaicin cream contains only a small amount of the active ingredient. Zostrix, for example, contains .025 percent capsaicin. Zostrix HP (for high potency) contains .075 percent. A mixture of capsaicin, oil and water, the cream disappears when it's rubbed into the skin.

Dr. Joel Bernstein, a Chicago dermatologist discovered capsaicin cream alleviated pain from shingles. To help develop it for easy use, he went to Lloyd Matheson, a University of Iowa pharmaceutical chemist, who formulated the cream in the late 1980s.

Then Bernstein founded Genderm and began promoting capsaicin products to relieve pain from other conditions. Medical researchers eventually picked up on its possibilities.

In a study at the University of California School of Medicine at San Diego, scientists found capsaicin not only depletes substance among arthritis patients, but also reduces prostaglandin, a chemical messenger that inflames joints.

And in another study, of 101 arthritis patients, about 70 percent reported pain relief after four weeks of use. What's more, nearly all the participants noted improvements in performing daily activities.

Dr. Ted Rooney, a rheumatologist with Mercy Hospital Medical Center' s Arthritis and Osteoporosis Center in Des Moines, Iowa, says he recommends Zostrix to his patients, though not all of them find it helpful.

``Because it is derived from hot peppers, they have trouble with the burning that can occur, and they give up on it quickly. Some people often have to use it five to seven days before it helps. But those people who get help with it get a lot of help,'' he says.

Alleviating cluster headaches is another condition that capsaicin cream may help. People who suffer from what's known as cluster headaches report dramatic relief from putting some capsaicin cream on a swab and applying it inside their nose, says Genderm's Verburg.

Moreover, a Yale University study indicates that a taffylike candy made with capsaicin reduced pain from sores and blisters that often develop in the mouth and esophagus of chemotherapy patients, he points out.

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Copyright 1996, Gannett News Service, a division of Gannett Co., Inc.