It is the sight we all dread, someone sniffling and sneezing, and you just know its going to head your way.
But how far exactly do you have to stand away from someone with a cold or flu to not catch what they are carrying?
Well, six feet away is the answer if they sneeze, so good luck if youre travelling on the underground.
Americas Centre for Disease Control and Prevention has researched how people contract coughs, colds and the flue and the sneeze is the most common culprit.
The CDCPs website warns: People with flu can spread it to others up to about six feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk.
These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.;
Out of all the human methods of spreading infection the sneeze is the turbo-propelled method, powered by human reflex, the projectile mucus can travel at speeds of up to 4.5 metres per second, compared to breath which travels about 1.4 metres per second.
Other ways people can be infected is by touching a surface which has the virus on it then touching their face, especially the mouth, nose and eyes.
Sharing a towel is also a sure-fire way of catching someone elses virus.
Also the more humid an area is, the better the chance of catching something nasty.
The CDC report adds: Most healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick.
Children and some people with weakened immune systems may pass the virus for longer than seven days.
Symptoms can begin about two days (but can range from one to four days) after the virus enters the body.
That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some people can be infected with the flu virus but have no symptoms.
During this time, those people may still spread the virus to others.
So if you spot a friend with the flu coming your way, the best option is to walk the other way.