Gesundheit!

Some 40 to 50 million Americans will contract the flu this season, and the number of cases of the common cold will top a billion. A good number of us will be nursing a cold three times this year. With all that sneezing and sniffling, it's easy to think that no one is immune.

Some people do seem to succumb more easily than do others. It takes just one cough in a crowded elevator to send the predisposed to bed with the familiar achy joints and runny noses. And they seem to be sicker for longer periods than their coworkers.

Although some people may be naturally more susceptible to the common cold than average a growing body of evidence suggests that the ease with which we are infected is directly related to the amount of stress in our lives. People who endure large amounts of long-term stress are more likely to become infected with a cold or flu, and suffer more from cold and flu symptoms.

Colds and flu seem to go hand in hand. So it makes sense that the causes of these common illnesses are similar. The common cold can be the result of one of 200 different viruses, nearly half of which medical researchers have yet to identify. A cold virus enters through the mucus of the nose, eyes or mouth. (The drier the weather, the easier for the virus to attack.) Once the virus has infected a cell, it takes over the cell's protein-making mechanism to produce new copies of the virus. The familiar cold symptoms—runny nose, sneezing and congestion—are the results of the body's attempts to fight the virus.

Like a cold, influenza—the flu—is also caused by a virus, but usually only a handful of different kinds in any given year. (That's why flu vaccines can be effective, because they give immunity against all the different strains that a person will probably encounter. A cold vaccine, however, would have to anticipate hundreds of different possible strains.) A flu virus also enters through the mouth or nose, and its symptoms appear within a few days of infection. The symptoms of the flu include fever, sore throat, aches, chills and exhaustion. And though the flu is generally just an annoyance, complications such as pneumonia can sometimes require hospitalization.

Colds and flu may be a yearly ordeal for some, but most Americans still have a lot to learn about treating them. A survey of 249 patients conducted by Barbara L. Braun, Ph.D., of the Park Nicollet Institute in Minneapolis, found that a majority believe that inhaling steam, a traditional remedy, helps in reducing cold symptoms, despite medical evidence to the contrary. And many people thought that antibiotics could help treat a cold—even though bacteria don't cause colds.

Fortunately most people were aware that over-the-counter medicines can do wonders for a cold. Although some antiviral drugs are effective in shortening the duration of flu, the National Institutes of Health advise a simpler and easier regimen for most people with colds and flu. The most effective treatment involves plenty of bed rest, drinking lots of fluids and taking over-the-counter remedies to ease the symptoms.

But why are some people more likely to come down with a cold in the first place? That's a question Sheldon Cohen, Ph.D., of Carnegie Mellon University in Pittsburgh asked. Cohen specializes in researching the way environmental stress affects human health and wanted to find a way to experimentally confirm some of the results he was seeing in the field. In a series of experiments, Cohen and his colleagues surveyed 256 volunteers about stress factors in their lives, then infected them with a cold virus. The researchers then watched how the volunteers' immune systems fought off the infection.

Cohen found that the most damaging kinds of stress are caused by long-term problems—the kind associated with a bad job or a rocky marriage. People suffering from such stress were twice as likely to come down with a cold. "The longer a stressful event has gone on," Cohen says, "the greater the effect it seems to have."

Researchers in Germany have shown that even short-term stress—such as a final exam period for college students—can reduce the amount of salivary Immunoglobulin A (sIgA), a chemical that serves as the body's first line of defense against infection.

Some healers have employed stress relief as a means to relieve the symptoms once the cold hits—or aid the body's ability to fight off infections in the first place. Aromatherapy, herbal preparations and yoga have all been tried, with varying degrees of success. But Cohen, for one, isn't sure that short-term stress-relief solutions are the answer to fighting colds. Cohen's advice for avoiding a cold this season? "Wash your hands."