In the twelfth century, the physician Moses Maimonides recommended removing milk and dairy products from the diet to help those with breathing or congestion problems. Traditional Chinese medicine also attributes increased ‘humidity’ or increased mucus production to eating too much dairy produce. Particularly for people suffering from asthma or breathing problems, the idea of eating mucus-producing foods may seem particularly dangerous.
Were these early physicians on track? Is avoiding milk key to avoiding problems with congestion or asthma or even just that phlegmy feeling? Scientists have put the question of dairy foods and mucus production to the test and found no evidence to suggest that milk or dairy products really increases mucus production.
One group of scientists took 125 people, randomly gave them cow’s milk or a soya drink, and measured their beliefs about the ‘milk mucus’ effect and their symptoms. All of the drinks were flavoured with cocoa and peppermint to make it impossible to tell who had the cow’s milk and who had the soya drink. Even the people conducting the study did not know who had which drink. In the end, there was no significant difference in problems like a ‘coating over the mouth’, ‘swallowing a lot’ or having ‘thicker saliva’ between those who had the milk and those who had the soya. Interestingly enough, the people who believed in advance that there was a ‘milk mucus’ effect reported more symptoms with both the soya beverage and the cow’s milk.
In another study, researchers took sixty adult volunteers, tried to make them ill with the common cold virus (once again, we’re amazed people agreed to do this) and then recorded their daily breathing symptoms and their milk intake over the next ten days. Of the fifty-one people who did get a cold, the weight of the nasal secretions did not increase in those who drank more milk. In fact, drinking milk was not associated with cough, nose symptoms or congestion, even in those with the cold virus.
One group of scientists did show that drinking milk or water increased how much spit or saliva you produce. However, the chemicals that make your saliva thicker were not increased. Furthermore, there were no differences in the mucus content of the saliva after drinking milk than after drinking water.
Still, many people (doctors included!) believe that drinking milk increases phlegm production. In a study of 330 parents, 58.5 per cent believed that drinking milk increases mucus production, and almost a third of them had been told this by their doctor. Seventy people who believed that milk caused increased mucus production reported experiencing clearing of the throat, coughing, swallowing, spitting and post-nasal drip because of drinking milk. However, in all of the aforementioned studies that we reviewed, there was no evidence that milk actually increases mucus production. One possible explanation for the increase in phlegm that some people think they experience after drinking milk is that the milk may lead to ‘droplet flocculation’ or spreading out of small milk droplets in the saliva. That sensation might be mistaken for mucus – but it’s nothing more than milk droplets mixing with saliva.