Does Drinking Milk Make Your Body Produce More Mucus?

January 21, 2021

A persistent myth about milk – that drinking it causes the body’s airways to produce more sticky mucus – is completely wrong, a new review finds.

The myth is so persistent that some parents have stopped giving milk to children with chronic respiratory conditions such as asthma and cystic fibrosis, out of fear that drinking milk might make it harder for their children to breathe.

But the milk-mucus link is just a myth, says review author Dr. Ian Balfour-Lynn, a pediatric pulmonologist at the Royal Brompton Hospital in London. And when people take that myth as real medical advice, it can have serious consequences.Balfour-Lynn says not giving children milk can make it difficult for them to get enough calcium, vitamins and calories. Children who don’t drink enough milk are also more likely to have broken bones and shorter stature, research shows.

It’s unclear exactly when the milk myth began. It could have come from Moses Maimonides (1135-1204), a philosopher and physician, who wrote that milk causes “stuffing of the head.” In addition, traditional Chinese medical texts link the consumption of dairy products to “humectant effects and thick phlegm,” writes Balfour-Lynn in a commentary published online yesterday  in the journal Archives of Disease in Childhood.

Even the influential book Dr. Spock’s Infant and Child Care (which has sold more than 50 million copies since its publication in 1946) repeats this claim. The 2011 edition of the book states, “Dairy products may cause more mucus complications and more discomfort from upper respiratory tract infections.” Balfour Lane found this when he researched this myth.

Given the influence of this myth, it is not surprising that, according to a 2003 study published in the journal Appetite, in a study of 345 randomly selected shoppers in Australia, 51 out of 111 whole milk drinkers (46%) “agreed” that milk causes mucus. However, the type of milk seemed to influence the shoppers’ decision. The study found that only 30 out of 121 reduced-fat milk drinkers (25%) and 12 out of 113 soy milk drinkers (11%) agreed with the statement.

This myth may persist because of milk’s unique properties. Milk is an emulsion, meaning it has droplets of one liquid suspended in another. (In the case of milk, the fat droplets are suspended in water.) When a person drinks milk, the milk mixes with their saliva.

Balfour-Lynn told Live Science that the sticky compounds in saliva can increase the viscosity, or thickness and volume, of milk. The resulting “feeling of thickness coating the mouth and after – when a small amount of emulsion remains in the mouth after swallowing” could lead people to believe that drinking milk causes a sudden spike in mucus, he noted.

Another potential explanation for the myth is that when milk breaks down, it releases a protein known to boost the activity of genes involved in mucus production. But this particular mucus production occurs in the gut, not the respiratory tract, says Balfour-Lane.

This mucus may affect the respiratory tract only if the gut is weakened by infection, which would allow the mucus to travel elsewhere in the body, he says. This doesn’t happen with the common cold, although it may affect people with cystic fibrosis, which is sometimes accompanied by intestinal inflammation, Balfour-Lynn said.

However, small studies dating back to 1948 have shown that drinking milk is not associated with an increase in respiratory mucus, he found.

In short, “Sure, the texture of milk can make some people feel their mucus and saliva is thicker and harder to swallow, but there is no evidence (and indeed there is evidence to the contrary) that milk causes excessive mucus production,” Balfour-Lynn writes in his commentary.” The milk-mucus myth needs to be firmly refuted by health care professionals.”

Dr. Corey Wasserman, a pediatrician at Weill Cornell Medical Center in New York City, who was not involved in the review, said the review is important because it helps raise awareness that drinking milk in the presence of respiratory problems is perfectly healthy.

It’s common to hear parents ask about milk myths during flu and cold season, Wasserman said. She tells patients exactly what this review found – that milk does not increase mucus or phlegm production. In addition, cold milk can help hydrate and soothe the throats of sick children who need calories, Wasserman told Live Science.