As far as colds go, there are over a hundred different viruses that can cause a common cold. That is why some people seem to get colds over and over all winter long. In general, a cold is contagious from about 24 hours before onset of symptoms until about 5 days after onset. You can catch a cold by inhaling airborne droplets or, more commonly, by touching a surface that contains the mucous or saliva of someone with a cold. That is why hand washing is so important. For more information on the common cold virus and natural remedies click here.