Do dairy products cause phlegm to build or thicken?

Question

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)?

Really? I never heard that one before. Instead I heard so many times that when you have a cold you should take a warm cup of milk with honey... — nico, Feb 05 '12 at 09:50
The link used to show notability for this claim says itself, "Some people think that milk increases mucus production or makes it thicker or harder to swallow, but this is likely not the case, according to the Australasian Society of Clinical Immunology and Allergy." It does not support the claim, but in fact claims the opposite. — Reinstate Monica -- notmaynard, Jun 15 '16 at 16:48

score 15 · Accepted Answer · edited Feb 05 '12 at 07:53

15

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.

edited Feb 05 '12 at 07:53

Oddthinking

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answered Feb 05 '12 at 07:03

nitwit

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So, two things about that study: one, they are studying people with increased mucus production already (ie, they have a cold)-- what about people who have no such additional component? Secondly, what about people who are lactose intolerant? Even scientists who get paid by dairy researchers (who also back up this claim, btw: http://www.ncbi.nlm.nih.gov/pubmed/2154152) must allow that those with milk allergies can still develop respiratory problems. – mmr Feb 05 '12 at 21:58
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I respond (despite a preponderance of articles that tell me that I'm wrong) because we've definitely noticed the effect in our 2 year old son, to the point that he's not allowed to drink milk. His breathing becomes so labored that he can't sleep. His uncle is similarly affected, and has tested positive to lactose intolerance. I know that anecdote != data, but at least in our house, there shall be no milk. Cheese, though, does not seem to be a problem, for whatever reason, so lactose might not be the ultimate cause. – mmr Feb 05 '12 at 22:01
I hate to argue with a well-researched answer, but the article cited explicitly cites "mucus" and not "phlegm". Indeed, there is no increase in mucus production (outside of expected results) that same Doctor was also quoted saying that the people might be describing a thick milk sensation on the back of their throat that they attribute to mucus. – TheCompWiz Feb 10 '12 at 17:05
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Regarding cheese: It doesn't harm people with lactose allergies because cheese is made by feeding milk to bacterial cultures. These cultures break down the lactose into something more digestible, so cheese has much less lactose than milk. – Noah Jul 25 '12 at 14:42
@Noah-- not so with mozzarella. With mozzarella (http://www.cheesemaking.com/howtomakemozzarellacheese.html/), just add acid to warm milk, and voila, cheese. This basis can then be fed to bacteria for other kinds of cheese, but not all cheeses have had their lactose bacterially reduced. If you make the cheese with lactose-reduced milk, then obviously the cheese has no lactose. – mmr Jul 25 '12 at 18:56
Most, but not all, of the lactose in milk is in the whey, which is deliberately removed when making cheese. But some does remain. Aged cheeses are usually essentially lactose free due to the culture eating what remains. Mozzarella is not aged, so it will strongly depend on the mechanical process success at whey removal and how much the curd is washed. – RBerteig Apr 29 '14 at 23:17
Lactose intolerance is not the same as dairy allergy. Lactose intolerance results from insufficient lactase which is needed to reduce lactose to a digestible form. Without it, lactose reaches and over-feeds otherwise beneficial gut cultures which then give off copious amounts of CO2, cause much discomfort, and make life very unpleasant until the bolus of lactose clears the gut. Allergies are an immune reaction, usually to specific proteins, and have different symptoms. – RBerteig Apr 29 '14 at 23:22
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@mmr, I don't think lactose intolerance/dairy allergy is relevant to this claim, which appears to refer to the population at large. – Brian S Apr 30 '14 at 14:22
@mmr Lactose intolerance isn't at all relevant to this claim. – Waterseas Apr 30 '14 at 14:56
The “Rules” of Singing: Mythbusters Edition claims it doesn't increase production but does cause it to thicken. – ChrisW Jun 06 '15 at 07:44
@mmr I came upon this question while researching the phenomenon because of our two year old son having the same issue. When we give him milk before bed, he snores and wakes up coughing. When we don't, he sleeps through the night. I don't think one study in adults with upper respiratory infections is sufficient evidence for an answer in the negative. – Andrew Oct 21 '17 at 23:59

Do dairy products cause phlegm to build or thicken?

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