A sneeze in progress, revealing the plume of salivary droplets as they are expelled in a large cone-shaped array from this man?s open mouth, dramatically illustrating the reason one needs to cover his/her mouth when coughing, or sneezing, in order to protect others from germ exposure. Illnesses like the flu (influenza) and colds are caused by viruses that infect the nose, throat, and lungs. The flu and colds usually spread from person to person when an infected person coughs or sneezes. Photo by