Human beings catch more colds than all other diseases combined, and people in the United States spend about $5 billion a year on doctor bills and over-the-counter relief from symptoms.

Despite the prevalence of colds, no one is sure exactly how colds are spread, according to an article in Esquire, a Hearst magazine, and no one has bottled a cure.Some researchers believe colds are spread by "aerosol" transmissions - you inhale someone else's germ-bearing sneeze droplets.

Others blame "hand-to-hand" transmission - you touch a surface with germs on it, then rub your own nose or eye.

Whatever the transmission method, there are as many as 200 known cold viruses and an unknown number of mutant varieties to come.

"Colds seem to inspire a strange, almost inexplicable national machismo," said Michael Castleman, author of "Cold Cures."

He said this leads people to go to work with a cold, thus releasing millions of virus particles and possibly infecting many others.

Castleman, editor of the magazine Medical Self-Care, has some predictions about the directions of cold research.

"Over the next couple of years," he said, "doctors are going to come around to vitamin C."

He said about half of previous tests indicated benefits and half did not. He said the studies in which vitamin C showed significant benefits used higher doses than the others.

Vitamin C is thought, even by scientists who don't believe in it as a cold cure, to boost the power of the immune system. Castleman believes the future of cold research lies not in blockbuster pharmaceuticals but toward subtler and more powerful enablers for the immune system, the body's own virus killer.

Upper respiratory infections come from viruses that belong to seven major families - one that causes influenza and six that cause colds. The rhinovirus family causes up to half of all colds.

Zinc may help against rhinovirus, although proof is meager, Castleman said. "The jury is still out," he said. The Food and Drug Administration prohibits medicinal claims for zinc. High doses can be toxic.

Antihistamines work for allergies but are useless against colds, declared a panel of ear, nose and throat specialists at Johns Hopkins and the universities of Virginia and Pittsburgh.

The real promoter of swelling and dripping in colds may be another substance released by injured cells - the kinin, particularly bradykinin. Castleman said kinin experiments could be the most exciting research on relieving common cold symptoms.

Castleman revealed his own regime for coping with cold - relaxation and visualization exercises. Studies at Harvard and elsewhere show that clearing your mind of outside cares and focusing your awareness on an inner place boosts secretions of antibodies such as immunoglobulin A.

He also takes a lot of vitamin C and drinks hot liquids - including chicken soup. Rest also helps.

"The first few days of a cold are the equivalent of hard physical labor," Castleman said. "The body can only do so many things at once."