The idea that the common cold and influenza are spread via coughing, sneezing, and physical contact has been firmly implanted in our minds since childhood. However, the results of human experiments cast doubt on this theory. Researchers have failed to consistently demonstrate contagion by exposing healthy people directly to sick people or their bodily fluids. These findings suggest that our understanding of infectious disease is incomplete and challenges the long-held belief that a cold or flu can be ‘caught’.