For decades, people suffering from a cold, flu, or sore throat have been told to avoid milk because it supposedly increases phlegm and worsens congestion. This enduring belief suggests that dairy products trigger the respiratory system to produce more thick, sticky mucus, making an already uncomfortable illness more difficult to manage. The advice has become so ingrained in popular culture that many people instinctively cut milk from their diet the moment they feel a tickle in their throat. This widespread practice is often based on the immediate sensation felt after consuming a beverage with a particular texture. Understanding whether this age-old wisdom holds up requires separating the sensory experience from the actual biological effect.
Addressing the Milk and Mucus Connection
The perception that milk creates excess mucus is a persistent myth, but scientific evidence generally does not support it. Controlled studies, including those where volunteers were infected with the common cold virus, found no statistically significant link between the consumption of milk or dairy products and an increase in nasal secretions or congestion symptoms. The respiratory system’s natural production of mucus, which already thickens during an infection, operates independently of milk consumption.
This widely reported sensation of increased phlegm is likely a sensory trick caused by the physical properties of the milk itself. Milk is an emulsion of fat and water, and when it mixes with saliva, it briefly creates a coating that lingers on the tongue and throat. This temporary coating increases the thickness and volume of the liquid mixture in the mouth, leading to a feeling often misinterpreted as a build-up of mucus.
In one study, subjects who strongly believed milk caused mucus reported similar symptoms of throat coating and thickness even when they drank a dairy-free soy beverage with a similar texture. This suggests that the belief itself influences the perception of symptoms more than the actual dairy content. Furthermore, a study involving children with asthma found no difference in breathing symptoms or mucus production whether they drank dairy milk or a soy alternative.
While the vast majority of research concludes that milk does not increase mucus production, a small number of studies have explored the possibility that certain milk components, such as beta-casomorphin-7, could potentially stimulate mucus production in a subgroup of individuals with underlying inflammation. However, the effect is complex and would require the presence of inflammation and the component entering the bloodstream. For the average person dealing with a cold, the current scientific consensus maintains that avoiding milk solely to reduce phlegm is unnecessary.
Digestive Tolerance During Illness
While the respiratory system is usually unaffected by milk, the gastrointestinal (GI) tract can present a separate set of challenges when you are sick. Illnesses that cause vomiting, diarrhea, or high fever, particularly stomach viruses like gastroenteritis, can temporarily damage the lining of the small intestine. This damage can lead to a temporary reduction in the production of the enzyme lactase, which is necessary to break down lactose, the sugar found in milk.
When lactase levels drop, the undigested lactose travels to the large intestine where gut bacteria ferment it, leading to secondary lactose intolerance. Symptoms of this temporary intolerance include abdominal bloating, gas, cramping, and loose, watery stools. These symptoms can compound the discomfort of an existing illness, making milk a poor choice even for people who normally tolerate dairy.
The severity of these digestive symptoms is often proportional to the amount of lactose consumed. Additionally, the fat content in whole milk can further delay gastric emptying. If nausea or vomiting is a concern, consuming any heavy or fatty food, including higher-fat dairy, may be ill-advised as it can exacerbate feelings of discomfort.
For individuals recovering from a GI illness, this secondary lactase deficiency is usually temporary, often resolving within a few weeks as the intestinal lining heals. During this recovery period, the best approach is to avoid traditional dairy milk or opt for lactose-free alternatives. Fermented dairy products like yogurt with active cultures may be better tolerated, as the fermentation process naturally reduces the lactose content.
Nutritional Considerations and Alternative Fluids
When the body is fighting an infection, maintaining caloric and nutrient intake is important for supporting the immune system and fueling recovery. Milk is a nutrient-dense beverage that offers several components beneficial during illness. A single cup of whole milk provides approximately eight grams of high-quality protein, which the body uses to build and repair tissues, including the cells of the immune system.
Milk also delivers several micronutrients that play a role in immune function, such as Vitamin A, Vitamin D, and zinc. Vitamin A helps maintain the protective mucous membranes that serve as the body’s first line of defense against pathogens. The protein, along with the other calories in milk, makes it an easily digestible source of energy when a person lacks the appetite for solid food.
For those who cannot tolerate milk due to temporary GI upset or a diagnosed allergy, prioritizing hydration and nutrients remains important. Clear liquids are often the best choice to replace fluids lost through fever, vomiting, or diarrhea.
Hydration Options
- Water
- Herbal teas
- Clear broths
- Electrolyte solutions
If a person needs to avoid dairy but still requires a source of calories and protein, fortified non-dairy milks, such as soy or oat milk, can serve as a substitute. These alternatives often contain added calcium and Vitamin D, and soy milk offers a comparable protein content to cow’s milk. Light, easily digestible soups and broths can also provide both fluids and necessary nutrients.