Busting the mucus myth: Turns out it’s OK to drink milk when you have a cold

Here’s how a brief note about milk and asthma, intended for an Egyptian sultan over 800 years ago, led to parents around the world eliminating milk from children's diets for centuries.

A new review of the milk-cold-phlegm connection, published in a BMJ journal this month, says it's okay for most kids to drink milk when they have a cold. Source: Moment RF/Getty Images

For hundreds of years, the sworn enemy of the common cold across all corners of the globe has been the luxurious white dairy queen, milk.

Warned not to drink milk while you have a cold as a child, many of us spent our sick days in youth, threatened by the fear that consuming the white stuff would generate horrid phlegm.

Children with asthma and cystic fibrosis were also cautioned to stay away from drinking milk because popular belief suggested it could worsen respiratory conditions.

But a new academic review of the milk-cold-phlegm connection, published in the BMJ journal Archives of Disease in Childhood this month, says the milk-mucus connection is nothing but a myth.

Children can drink milk when they have a cold and it will not generate extra phlegm – not even if they have asthma, cystic fibrosis or a respiratory condition. Better yet, the review says, consuming milk is recommended for most children because it is a nutritious source of protein and vitamins.

It's okay for kids with asthma or a cold to drink milk. (Getty Images) Source: Photographer's Choice/Getty Images

So where did the myth start?

It turns out that the milk-mucus myth was actually a product of Jewish, Egyptian and Chinese happenings, and more recently, popularised medical claims from the USA.

Experts think that the myth unintentionally originated in Egypt over 814 years ago. The review's author – children's respiratory consultant Dr Ian Balfour-Lynn of London’s Royal Brompton Hospital – explains that a Jewish spiritual leader and Egyptian court physician, Moses Maimonides first wrote about the milk-mucus link while trying to help a sultan.

But the truth is that Maimonides’s writings were never just about milk and mucus and his advice may have been taken out of context.

“In his Treatise on Asthma, written for an asthmatic relative of Saladin the Great, he warns against eating several foods that generate phlegm,” Dr Balfour-Lynn writes in his review.

Saladin the Great was the first sultan of Egypt and Syria and the founder of the Ayyubid dynasty.

However, while he warns against cheese (especially if very old), his only mention of milk is that all kinds cause ‘a stuffing in the head’ and it is best to keep away from them.

“These include fatty food; scalding hot gas-generating foods (for example, black beans, peas); food made from coarse wheat flour and heavy meats.

"However, while he warns against cheese (especially if very old), his only mention of milk is that all kinds cause ‘a stuffing in the head’ and it is best to keep away from them.”

The review also notes that traditional Chinese medical texts have linked dairy consumption with a humidifying effect and thicker phlegm, “although in reality most of their texts are positive about drinking milk”.

Maimonides’s mention somehow lingered over the centuries and persisted as fact in various cultures. The real turning point occurred when the myth was included in the influential book from the USA, Dr Spock Baby and Child Care.

The book, first published in 1946, suggested that milk may aggravate asthma and other respiratory problems so parents should remove milk from their child’s diet altogether. It’s estimated that the book had sold more than 50 million copies by the time of Dr Spock’s death in 1998.

A study, published in 2012, states that even though there is limited scientific evidence to link milk consumption and asthma, many parents still believe the myth.

Meanwhile, current advice from the Australian Society of Clinical Immunology and Allergy, confirms that the milk-mucus link is not accurate.

“Some people complain that when they drink milk or other dairy products, their throat feels coated and mucus is thicker and harder to swallow,” the organisation says online. “Recent research has shown that these feelings are due to the texture of the fluid and occur with similar liquids of the same thickness, and are not due to increased production of mucus.”

The body concludes that eliminating milk from a child’s diet does not help asthma and that milk has no effect on lung capacity. In fact, any improvement in mucus production or respiratory capacity resulting from eliminating milk could be a placebo effect.

Australian research dating back 25 years also shows that people who believe in the “milk-mucus theory” may have more asthma-related symptoms than people who don’t. As part of the 1993 study, researchers surveyed 130 participants. People who believed in the myth reported drinking considerably less milk than nonbelievers and yet they still said they experienced more respiratory symptoms.

So technically, although there’s not a lot of hard evidence to suggest that drinking milk while you have a cold or suffer from a respiratory condition could make you develop more mucus, believing in an 800-year-old cultural myth just might.