The belief has persisted for centuries that ingestion of milk causes excessive mucus, although the few studies on the topic have failed to demonstrate any effects of milk on mucus production.1- 3 The objectives of this study were to ascertain the prevalence and sources of this belief in parents; whether parents were more likely to believe that milk causes mucus if their children had allergies, asthma, or cystic fibrosis; and whether this belief altered their children's diets.
Lee C, Dozor AJ. Do You Believe Milk Makes Mucus?. Arch Pediatr Adolesc Med. 2004;158(6):601-603. doi:10.1001/archpedi.158.6.601-b