This is a MYTH.
Perhaps you’ve conducted your own empirical evidence and don’t believe us. After all, every time you get a cold and drink a glass of milk you could swear your nose runs a little bit more and your cough gets worse. You’re not alone when it comes to believing this milk myth. A study of 330 patients found that two-thirds believed milk causes phlegm, worsening an already runny nose and coating your throat with mucus. Turns out those 220 people were wrong: The theory that milk causes phlegm has been debunked by research time and time again.
Milk and Mucus Have No Link
Australian researchers inoculated 60 patients with the common cold virus and tracked milk and dairy intake for ten days. The amount of milk consumed ranged from zero to 11 glasses a day. When asked, “does milk cause mucus” patients reported symptoms of increased phlegm. However, when researchers collected and weighed nasal secretions, they found no link between milk consumption and mucus production. A 2005 meta-analysis of studies likewise found no association between milk and mucus.
Why did patients report feeling more phlegmy? Scientists theorize that the texture and viscosity of milk may be deceiving people into believing that milk is increasing mucus production, which is not actually the case.
What Causes Mucus Mania?
Increased mucus production is rarely caused by diet and is more than likely caused by viral infections, allergies and medications that dry out the throat and mouth. There has really only been one study that creates a link between milk and mucus. Published in the journal Medical Hypotheses—a publication noted for its support of radical biomedical theories—the study showed that milk from specific breeds of cow contains a protein known as beta-CM-7. This protein has been shown to spark mucus glands in both the digestive and upper respiratory tracts. If this protein does indeed lurk in certain brands of milk, then it would account for why a small percentage of individuals who suffer from increased phlegm in the upper respiratory tract (such as those with asthma), tend to improve when placed on a dairy-elimination diet.
Keep in mind, however, that this was one study out of many that profess otherwise, and that cutting out dairy can have adverse health consequences. After all, a glass of milk a day strengthens bones and keeps the orthopedist away. Not to mention, milk fortified with vitamin D gives you an extra jolt of energy to carry you through your day, encourages cell growth and fortifies your immune system.