Colds are caused by viruses. These are much smaller “bugs” than bacteria. It’s widely believed before we knew what viruses are, that the illness known as the common cold was caused by exposure to cold weather since that’s the time of year that cold and influenza viruses are more active. However, cold doesn’t cause a cold or flu, but the decreased humidity in the air during the cold time of year allows the cold viruses to be more active. When humidity is high these viruses are less active. Also when it’s cold outside people tend to crowd inside making it easier to share the virus.
Children with the virus can cough, sneeze or touch their nose and get some virus on their hands. Then they touch the hand of another person who touches their nose and the virus starts to multiply and a cold develops.