Think of coughing as a defense mechanism designed to rid your lungs and windpipe of substances that don't belong there. In the case of colds, this intruder is usually mucus, which builds up more than the airways can comfortably handle. At other times, the foreign substance might be something irritating, like smoke or pollution that has gotten trapped in the flypaper-like coating of the air passages.
So What Is a Cough?
First, your body senses an irritant, so the nerves in the lungs send an intruder-alert message to your brain. The brain responds by telling you to take a breath and close the epiglottis -- the small flap behind the tongue that seals off the windpipe. This causes a tremendous amount of air pressure to build up in the lungs. The chest muscles get tighter and tighter until the epiglottis is forced open, releasing the pressure in a noisy propulsion of air. In other words, you cough.
And just how forcefully do you expel air -- and with it foreign substances, such as droplets of flu virus? Well, let's just say that moving at 4 to 64 miles per hour, those droplets could get a speeding ticket.
Because you can also cough on command (such as when you clear your throat), coughing is not totally a reflex, says Schachter, who is also a professor of pulmonary medicine at Mount Sinai School of Medicine in New York City. But coughing is one of the top reasons people visit their doctors. When his patients come in to see him about their coughs, what is the No. 1 question they ask? "Is it good that I'm coughing something up? Or is bad that I'm coughing something up?" And he explains, "Well, if you've got mucus in your airways, it's good that you're coughing it up because bacteria just love to grow on [mucus]." But on the other hand, he says, "If you have an irritation and your chest is clear, then it's not necessarily advantageous to produce a lot of mucus."