There's no such thing as stomach flu. And no, you shouldn't starve a fever.

With winter in full swing, Americans are sniffling and sneezing by the millions, falling prey to flu, colds, strep throat and other common illnesses of the season. Yet most know little about what is making them sick or how best to treat their illnesses.

"People have a real misunderstanding about what causes their symptoms," says Dr. Jim Martin of San Antonio, president-elect of the American Academy of Family Physicians. "And most of us are not very sophisticated about which problems are serious ones that require a doctor visit."

Two of the season's most dreaded illnesses, cold and flu, are also two of the most misunderstood. Many people use the terms "flu" and "cold" interchangeably, although they are very different diseases.

Flu is a harsher illness that can lead to dangerous complications, such as pneumonia, in the elderly and those with weak immune systems. In general, flu hits harder and faster than a cold. A sudden high fever and severe body aches are its hallmarks.

Colds, meanwhile, are usually heralded by sneezing, congestion and a low-grade fever (or none at all). Complications are generally less serious. "True flu is almost always an acute process," says Martin.

People often complain of "stomach flu," an illness that, strictly speaking, doesn't exist. The influenza virus that causes flu affects only the respiratory (breathing) system, not the digestive tract. Upset stomachs are caused by other germs, including a variety of viruses and food-borne bacteria.

Patients are often misinformed about what leads to illness in winter. Whatever your parents told you, you can't get sick merely by walking outside in cold weather without a hat, or from having a wet head or feet.

Colds, flu, strep throat and other common illnesses are passed through contact - for example, touching a computer keyboard, doorknob or telephone after a sick person has used it, or sitting next to someone who is coughing and sniffling on a bus.

Exposure to a cold environment can make people vulnerable to illness in extreme cases, such as falling into icy water or being stranded outdoors in a blizzard. "If you get chilled enough, some of the immune systems in your lungs might not work as well," says cold expert Dr. Jack Gwaltney of the University of Virginia School of Medicine.

But even then, viruses and bacteria - not the cold environment itself - are the true culprits.

Popular wisdom on how to treat winter illnesses ranges from the absurd to the potentially harmful.

One adage, "starve a fever, feed a cold" - or is it the other way around? - has no merit whatsoever, doctors say. The idea of depriving any sick person of food is "totally off the wall," says Gwaltney. "I have no idea where that came from."

It's best to maintain a steady, nutritious diet during bouts with both cold and fever-inducing illnesses, he says.

Often, people who are sick with flu or a cold press their doctors for antibiotics, in the hopes of a speedier recovery. But colds and flu are caused by viruses, not bacteria, so antibiotics are useless in treating them.

Worse, overusing drugs helps germs develop defenses against treatment. "We don't want to help the bugs any more than we have to," says Gwaltney. Doctors and patients should use antibiotics to treat only true bacterial infections, such as strep throat and some types of pneumonia, he says.

Unpleasant as they are, symptoms such as fever and coughing are often best left to run their course. A low-grade fever is the body's way of "burning off" offending germs, and coughing helps clear the lungs of infected secretions.

Still, some doctors say, an occasional swig of cough suppressant can't hurt if a persistent hack is interfering with sleep.

In fact, rest and drinking plenty of fluids remain the cornerstones of a speedy recovery. The more rest a person gets, the more energy his or her body has to make immune-system regulators, such as interferon. "If you go out and run for three miles, your body isn't going to be able to make as much interferon," Martin says.

Fluids help flush infected cells from the body and help the kidneys function more efficiently.

In recent years, many Americans have enlisted over-the-counter remedies such as zinc and echinacea in their battles with colds and flu. Experts are divided on whether those treatments work, however. Martin says he wouldn't prescribe herbal remedies to patients, because studies on their effectiveness have been inconclusive. But he wouldn't expressly advise people not to take them, either.

Vitamin C, that granddaddy of home remedies, gets mixed reviews. Some studies have shown that it can shorten the duration of illness, while others say it neither prevents nor helps alleviate symptoms.

Medical experts say prevention remains the best treatment. Flu shots are a good idea, particularly for the elderly and chronically ill. Otherwise, Martin says, "just do what you learned in the eighth grade"  cover your mouth when you cough, wash your hands after touching shared property and maintain a healthy diet.