The claim that milk creates mucus or phlegm that may or may not be the result of a milk allergy has been around for years, so I suppose that it's not surprising that we'll need years to dispel it. I keep trying. I posted Udder Confusion in 2006 and Milk: No Mucus, No Asthma in 2007 so it's time to attack the myth yet again.
I'm getting help from Dr Raymond Mullins, an allergy specialist interviewed by Genelle Weule for ABC.net.au.
[W]hile many people swear milk produces mucus, the effect can't be explained by science, says allergy specialist Dr Ray Mullins.
A 2005 review of studies concluded that there was no link between milk consumption and mucus production or asthma. In one study, participants infected with the common cold virus reported symptoms of increased in mucus production after drinking milk, but when their mucus production was actually measured there was no statistical difference. In another study, there was no difference in the sensation experienced between drinking soy milk and cow's milk.
This doesn't mean people don't experience the sensation, says Mullins, but rather that there is no actual increase in mucus production.
He puts the sensation down to the texture and viscosity of milk, and notes that most people do not report similar effects with other dairy products such as cheese.
If you believe that milk will cause mucus, then any feelings of mucus you get from milk will simply reinforce that belief whether or not any true increase is present.
There's no scientific connection, though, nothing that can be found in theory or isolated in tests. If you can drink milk, then know the facts about it and make your own decisions based on those facts, not unfounded beliefs.