Nurse Gail Ingram answers the question, “Does dairy make a cold worse?” and discusses the milk-mucus myth:
I can’t count how many times I’ve heard that dairy products increase the symptoms of a cold or the flu. In fact, I had heard it so often growing up that I believed it myself. The truth is, it’s just a myth.
There is plenty of research to confirm that dairy products do not impact the symptoms of a cold. Back in 1990, researchers infected volunteers with a cold virus and monitored their dairy intake and measured their nasal secretions. The authors of the study concluded that there is no relationship between milk or dairy and mucus production in adults with a rhinovirus infection.
In 1993, study participants who believed in the milk-mucus myth were asked to drink non-dairy soy milk (that they were told was cow’s milk) and, sure enough, they reported increased symptoms. On a survey, participants reported sensations from very small amounts of milk with increased mucus occurring almost immediately. However, this is a result of the placebo effect since the body cannot produce mucus that quickly under those circumstances.
A 2005 analysis clearly states that milk consumption does not lead to mucus production or the occurrence of asthma. The authors did mention that people who suffer milk allergies may experience asthma-like symptoms (with or without the presence of a cold). But in 2010, it was shown that only a subset of people who have an allergy to milk experience increased mucus after consuming dairy. Among those people, many factors must be present, and even then, it isn’t a simple cause and effect situation.
So you see, the belief that milk increases mucus is what makes a cold worse; not the milk. I’m not recommending that you eat a gallon of ice cream the next time you get sick, but you certainly don’t have to be afraid of it.