In order to catch a cold, you must be exposed to someone with it or a surface they've touched and contaminated with the viruses (there are more than 200 types). You need prolonged and close contact with another person with a cold to go down with it yourself as colds are actually not very contagious. But aerosol transmission is the most effective method – if droplets from a sneeze enter someone else's eye or nose, there's a risk of infection. And those sneezes are powerful, with particles of mucus hanging around a room long after the sneezer has gone. So the only sure way to avoid a cold is to avoid human contact. And to use hand sanitisers to help protect against any viruses that may be hanging around surfaces such as door handles as well as regular hand washing.