A German scientist studying thousands of soldiers during World War I reported that those stationed in cold, wet trenches for 72 hours were four times as likely to develop colds as those kept in their barracks.

Mounties in the Canadian Arctic developed more colds and more severe colds during periods of unusual exertion in cold day and night conditions.

Among volunteers inoculated with a cold virus, those who reported life stresses that continued for more than one month like unemployment or family problems were more likely to develop colds than those who reported stress lasting less than a month.

People with higher social support are also less likely to develop colds and are able to recover faster if they are ill from a cold.

He also suggests less than 30 minutes of daily exercise to boost your immune system so you are less likely to develop colds and infections.

In a study published in 1991, psychologist Sheldon Cohen, Ph.D., of Carnegie Mellon University, injected nearly 400 healthy subjects with a cold virus, and found that those who reported more stress in their lives were more likely to develop colds.

Schoolteachers, parents of young children, and others who develop frequent colds also are at greater risk.