The mechanics of a cold.

When I get a cold, it starts as a stuffy nose, then adds a sore throat, plugged up sinuses and finally, coughing up flem that seems to build up in my lungs.

Is the flem I cough up independently created in my lungs? Is it carried into my lungs from my sinuses when I breath? Does it come from someplace else?

Your lungs produce the mucus. Sure, you’ll hack up some sinus drippings that have parked themselves in your throat, but when you hear the lungs wheezing, the mucus is made in the lungs.