Should You Avoid Dairy When You Have a Cold?

At some point, you have probably heard that you should avoid consuming dairy products when you have a cold because milk creates mucus. While this may sound like an old wive's tale, there may be some truth to it. However, science on the matter is still inconclusive.

For people with a milk allergy, congestion and increased mucus production is a common reaction. However, for most other people, drinking milk with a cold may only make phlegm feel worse because milk coats the mucus, making it feel thicker.

What Causes Mucus?

Colds, the flu, and other upper respiratory infections cause a runny nose, congestion, coughing, sore throat, and sometimes fever in response to the virus invading the body.

Essentially, these symptoms are a defense mechanism—a way that your body tries to get rid of what's making you sick. Increased mucus production is one way your body fights infection, and even though it's no fun to deal with, it actually does serve a purpose: The foreign invader becomes bound up in the mucus and expelled when you cough up phlegm or blow your nose.

What the Science Says

Whether or not drinking milk contributes to congestion is still up for debate. Some early studies designed to test the theory that dairy products increase mucus production found that it does not.

One study measured mucus production by weighing tissues after people blew their noses into them and found that dairy had no effect on expelled mucus volume.

Another study tested how people felt after drinking either cow's milk or soy milk, and the results were the same. The participants did not know which type of milk they were drinking but reported very similar symptoms.

While both studies concluded that there is no evidence that dairy has an impact on mucus production, newer research suggests otherwise.

A 2019 study found that a dairy-free diet may indeed reduce mucus. Researchers randomly assigned 108 people to either did or did not contain dairy for six days and found self-reported levels of congestion were lower in the dairy-free group. However, this study did not examine people with a cold or any type of virus—just people who complained of excess mucus production.

Other research hypothesized that the effect milk has on mucus production depends on the person’s genetic makeup and the type of dairy protein. The theory is that A1 casein protein, typically found in cow’s milk, stimulates mucus production in the intestines in some individuals, which circulates throughout the body leading to congestion.

This research, however, is limited, and human studies are needed before concluding a genetic link.

Treating Mucus

One of the best things you can do to relieve congestion and excess mucus is to stay hydrated. Drinking water, running a humidifier, using a saline nasal spray, and rinsing sinuses with a neti pot can help thin mucus, making it easier to expel.

There are also over-the-counter medications like decongestants and expectorants that can help break up mucus and allow it to drain from your sinuses or be expelled through coughing.