Phlegm is the thick, sticky mucus that drips down the back of your throat when you have a cold. Although drinking milk may make phlegm thicker and more irritating to your throat than it would normally be, milk doesn't cause your body to make more phlegm. Studies have found milk intake was not associated with increased nasal secretions, coughing, nose symptoms or congestion. Some doctors say that milk thickens saliva, which may coat the throat and give the perception of more mucus, but it does not cause the body to produce more mucus or phlegm.
Postnasal drip also commonly causes excess mucus at the back of your nose and throat many times after eating. Excessive, thick phlegm or chest mucus can often be caused by viral or bacterial infections such as influenza, bronchitis and pneumonia, as well as irritants such as those inhaled during smoking.
Hacking coughs and endless throat clearing are problems that can be greatly helped by improving general lung health.
There’s absolutely no truth to the idea that milk increases mucus production, so there’s no need to skip it when you feel congested. Furthermore, milk may actually contribute to speeding up recovery, as drinking lots of fluids when you have a cold is important.