What is a milk allergy?

little girl drinking a glass of milk
(Image credit: Getty Images)

Cow’s milk allergy is one of the most common food allergies in infants and adults, but not many people know what causes it or how it shows. Milk allergy is sometimes confused with lactose intolerance, but while these conditions are both triggered by consuming dairy products, they don’t share the same causes or symptoms. They also require different treatments. 

If someone has a milk allergy, their immune system considers certain proteins in cow’s milk as invaders. In order to neutralize this perceived danger, it initiates a potentially life-threatening allergic reaction. Lactose intolerance, on the other hand, is rooted in problems with breaking down and digesting lactose, which is the main sugar found in dairy products. 

As milk allergy tends to manifest in infancy, knowing how to recognize the symptoms early on is important for parents and carers. We’ve created a guide to milk allergy to help you have a better understanding of the causes, symptoms and treatment options for this common condition.

What is a milk allergy?

According to the National Institute for Health and Care Excellence, milk allergy is an immune-mediated allergic response to one or more proteins in cow's milk, such as casein and whey. There are three different types of milk allergy, depending on the underlying immune mechanism and timing of symptoms: (Ig)E-mediated, mixed IgE and non-IgE mediated. 

An immunoglobulin (Ig)E-mediated allergy happens when a person starts producing serum-specific IgE antibodies immediately after being exposed to trigger proteins. This type of milk allergy produces instant and consistently reproducible symptoms. Adverse reactions typically occur up to two hours after eating dairy products, but usually within 20–30 minutes. 

A non-IgE-mediated food allergy does not involve the production of specific antibodies and reactions to this type of milk allergy are typically delayed. They usually manifest between two and 72 hours after the ingestion of cow’s milk. Mixed IgE and non-IgE allergic reactions involve a combination of IgE and non-IgE responses and are usually delayed.

image shows a man shopping for milk with his daughter

(Image credit: Getty Images)

Lactose intolerance happens when your body is unable to properly digest lactose. Lactose cannot be absorbed in the body in its primal form – it needs to be broken down to glucose and galactose first. The digestive enzyme responsible for this is called lactase. One of the main reasons behind lactose intolerance is the inability to produce enough of this compound. As a result, undigested cow’s milk sugar passes to the colon, where it’s taken up by intestinal bacteria. This process increases the amount of fluid and gas in the gastrointestinal system, causing symptoms like diarrhea, flatulence, bloating, stomach cramps and fatigue. 

It’s estimated that between 2% and 3% of children below the age of three are allergic to cow’s milk. According to the National Institute for Health and Care Excellence, risk factors include sex (boys are twice as likely to suffer from milk allergy than girls), atopic conditions (such as asthma and atopic eczema), a family history of food allergy and/or family history of atopy. Some may also cross-react to proteins found in goat, ewe, horse, camel, and buffalo milk.   

Milk allergy: causes and symptoms

According to the National Institute of Health and Care Excellence, the underlying mechanism behind milk allergy is not known, but it is thought that various genetic and environmental factors may play a part. Immunoglobulin (Ig)E-mediated cow's milk allergy is expressed by the production of specific IgE antibodies in response to cow's milk proteins. These antibodies bind to the surface of cells in the body, causing a release of cell mediators (such as histamine) that directly trigger the onset of the clinical symptoms. Whereas non-IgE-mediated cow's milk allergy is thought to be mediated by malfunctioning T-cells – a type of white blood cells essential to the functioning of a healthy immune system

According to The American College of Allergy, Asthma and Immunology, common milk allergy symptoms include hives (an itchy rash), upset stomach, vomiting, bloody stools and in the most severe cases, anaphylaxis. Symptoms of anaphylaxis include swelling of the airways, reduced ability to breathe, and a sudden drop in blood pressure, causing dizziness and fainting. 

How can you treat a milk allergy?

If you suspect that your child may be suffering from a milk allergy, it’s essential to consult a medical professional and obtain a correct diagnosis. Your doctor will ask questions to get a good understanding of your child’s medical history. They may also perform tests that can detect the presence of immunoglobulin E (IgE) antibodies, such as skin-prick or blood tests. 

Your doctor may also ask for your permission to do a test called an oral food challenge. Under stringent medical supervision, your child will be given small amounts of a substance containing milk proteins to see if any reaction develops. Your doctor will be able to confirm the diagnosis based on all of the collected measurements.  

young girl holding a glass of milk

(Image credit: Getty Images)

There are no effective pharmaceutical treatments for cow’s milk allergy. The only way to effectively manage this condition is to avoid dairy products and foods containing cow’s milk proteins. 

Under the Food Allergen Labeling and Consumer Protection Act of 2004, food manufacturers in the US are legally required to include the presence of cow’s milk and cow’s milk components on their ingredient labels. 

If your baby is too little to eat solid foods, your doctor or dietician will recommend you the most suitable baby formulas. To prevent anaphylaxis, patients with milk allergy (or their carers) are advised to carry a so-called EpiPen: an auto-injector containing epinephrine (adrenaline). Immediate application of EpiPen is the only treatment that can stop the life-threatening symptoms of anaphylactic shock. 

Another dietary modification that could help some with milk allergy is using baked cow’s milk. Baked milk refers to milk that has been extensively heated to disrupt the structure of the allergen proteins. Results from a 2017 study suggest that the majority of children under the age of two can tolerate baked milk products in their diet. Some studies indicate that drinking baked milk could help them outgrow their milk allergy quicker. But according to a review published in The Clinical and Experimental Allergy journal, there is little evidence to support this claim.

Can you grow out of a milk allergy?

According to a review published in the Nutrients journal, up to 75% of affected children will eventually outgrow a milk allergy by the time they’re five years old. Milk allergy symptoms are most likely to continue in those who have high levels of cow’s milk antibodies in their blood. Your doctor will be able to advise you if and when is the right time to reintroduce dairy products into your child’s diet. 

As children outgrow their milk allergy, they begin to tolerate lightly cooked milk and fermented dairy products. The quantity of cow’s milk that is safe often gradually increases. However, the speed of recovery and the amounts that are tolerated can vary significantly between different individuals. To minimize the chances of adverse reactions, it’s always good practice to reintroduce dairy products following a consultation with a medical professional or dietician. 

This article is for informational purposes only and is not meant to offer medical advice.

Anna Gora
Health Writer

Anna Gora is a health writer at Live Science, having previously worked across Coach, Fit&Well, T3, TechRadar and Tom's Guide. She is a certified personal trainer, nutritionist and health coach with nearly 10 years of professional experience. Anna holds a Bachelor's degree in Nutrition from the Warsaw University of Life Sciences, a Master’s degree in Nutrition, Physical Activity & Public Health from the University of Bristol, as well as various health coaching certificates. She is passionate about empowering people to live a healthy lifestyle and promoting the benefits of a plant-based diet.