Many patients note that dairy products, milk in particular, causes increased mucus or phlegm production. But does milk actually do this?. Even if it does, it is not an allergic reaction to the milk. It is important to remember that an allergic reaction to a food is defined as an immune reaction to that food. If it is not an immune reaction, it is not an allergy.
Several allergists have been having an interesting discussion about this on Twitter over the last day or so:
Dr. John Weiner @AllergyNet
Dr. Ves Dimov @Allergy
Dr. Anne Ellis @DrAnneEllis
Dr. Nathan Hare @AllergyTalk (me)
From the published articles in the medical literature, so far, the consensus is that milk does not actually produce an increase in phlegm / mucus. One intriguing study suggests a hypothesis for why a certain portion of the population could have a problem with milk.