What Is the Difference Between Lactose Intolerance and Dairy Allergy?

Glass of milk with caution sign
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People often talk about dairy allergies as though they are lactose intolerant, but aren't the two different? Lactose intolerance and a dairy allergy (also often referred to as milk allergy) are actually quite different, and the main differences have to do with the body's response to consuming the dairy product and the parts of the dairy that we are talking about.


Lactose intolerance refers to the inability to properly digest and metabolize lactose, which is the disaccharide (sugar) component in milk. This inability is the result of a deficient amount of lactase, the naturally-occurring enzyme needed to break down lactose, in the small intestine. People with lactose intolerance often suffer different levels of uncomfortable symptoms such as bloating and other gastrointestinal issues, but the symptoms are not life-threatening or as debilitating as those associated with milk allergies.

Casein vs. Whey

A milk allergy or dairy allergy, however, is more serious as it involves the immune system. And milk allergies are fairly prevalent, too, though not as prevalent as lactose intolerance. According to FARE (Food Allergy Research and Education), allergies to dairy are the most common food allergies in infants and young children. A milk allergy is an overreaction of the immune system to a specific protein, which then causes the body to react with any number of symptoms, which can range from mild to serious. People can experience hives, wheezing, vomiting, gastrointestinal issues such as diarrhea, or in some rare cases, even anaphylaxis. (This is why it's also important to know the difference between lactose-free and dairy-free when label-reading.)

A person with a milk allergy will often be allergic to one of two main proteins in milk: casein or whey (these, again, are different than the sugar component lactose).

Diagnosing Milk Allergies and Lactose Intolerance

Lactose intolerance can be hard to diagnose, but a doctor may ask you to keep a food diary to try to identify what foods give you the negative digestive symptoms. To diagnose a food allergy, a doctor can identify a blood test and/or skin test, and if the test cannot confirm a food allergy, they may try to administer an oral food test, in which you are fed different foods (including dairy) to see which cause the reaction.

Once you have a diagnosis, it's time to start living the dairy-free lifestyle like so many people and cultures already do. It's easier than you think to go dairy-free, and then start finding dairy-free versions of your favorite recipes.

Article Sources
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  1. National Institutes of Health. Symptoms & causes of lactose intolerance. February 2018.

  2. Food Allergy Research and Education. Milk allergy.

  3. American College of Allergy, Asthma & Immunology. Milk & dairy allergy. Updated March 21, 2019.

  4. KidsHealth from Nemours. Food allergies. Updated August 2018.