William Wells a scientist who studied tuberculosis transmission in the 1930s stated that when you exhale, sneeze, or cough, you release a cloud of gas and liquid droplets.

 

The heavier droplets will fall to the ground as raindrops do. If there are germs in that droplet, they can alight onto surfaces where they can be transmitted to people who unwittingly put their hand on the surface.

 

This view is now considered outdated and the actual picture is a lot more complicated. We are all always exhaling a gas cloud that contains within it a spectrum of droplet sizes. If propelled by a cough or a sneeze, droplets can travel upward of twenty feet.