Do dairy products cause phlegm to build or thicken? It is a common advice, perpetuated by many parents, and even some doctors, that if you have a cold, you should avoid dairy products, because they cause phlegm to build up or thicken. See e.g. Foods that cause mucus buildup. Do they (and if they do, how/why)?

The Wikipedia article List of common misconceptions states:

> Drinking milk or consuming other dairy products does not increase mucus production. As a result, they do not need to be avoided by those suffering from flu or cold congestion.

They back it up with this article:

* Pinnock CB, Graham NM, Mylvaganam A, Douglas RM. Relationship between milk intake and mucus production in adult volunteers challenged with rhinovirus-2. Am Rev Respir Dis. 1990 Feb;141(2):352-6.



which claims:

> Milk and dairy product intake was not associated with an increase in upper or lower respiratory tract symptoms of congestion or nasal secretion weight. [...] We conclude that no statistically significant overall association can be detected between milk and dairy product intake and symptoms of mucus production in healthy adults, either asymptomatic or symptomatic, with rhinovirus infection.