With my existing cold, I have had the pleasure of biting my tongue as well intentioned people have offered all kinds of advice and suggestions of how to take care of myself. The most repeated of these helpful tips is, "Don't have any dairy, it causes mucus."
For the last time, dairy doesn't cause mucus! If you won't take my word for it, here's the research (click the links to see the webpages the info was pulled from);
Robert H Shmerling, M.D. "I couldn't think of a reason why dairy products should be avoided in kids who recently had a cold. And it was certainly nothing I'd ever learned in medical school.
A remarkable set of studies published in 1990 found no clear connection between milk consumption and cold symptoms."
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. In fact, frozen dairy products can soothe a sore throat and provide calories when you otherwise may not eat.
PubMed.gov ( US National Library of Medicine National Institutes of Health )
Milk and dairy product intake was not associated with an increase in upper or lower respiratory tract symptoms of congestion or nasal secretion weight.
Milk consumption does not lead to mucus production or occurrence of asthma.
WebMD - The truth about mucus
Even when you're healthy, your body is a mucus-making machine, churning out about 1 to 1.5 liters of the stuff every day. Most of that mucus trickles down your throat and you don't even notice it.
It generally takes a bad cold, allergy, or contact with something irritating -- like a plate of nuclear-hot Buffalo wings -- to throw your body's mucus production into overdrive.
But mucus is more than just sticky goo. It also contains antibodies that help the body recognize invaders like bacteria and viruses, enzymes that kill the invaders it traps, protein to make the mucus gooey and stringy and very inhospitable, and a variety of cells, among other things.
Drinking milk may also make some people produce more mucus. Kao says that's due to gustatory rhinitis, a reflex reaction that's triggered by eating. Gustatory rhinitis is also why your nose runs when you eat hot peppers. Milk proteins cause the same type of response in some people. But although you may feel like you have more phlegm, you're not going to worsen a cold by drinking a glass of milk, Johns says.