Is lactose intolerance an allergy?

Contrary to popular belief, lactose intolerance is not an allergy and isn't considered to be the same medical condition as a dairy or milk allergy. Eating dairy products will lead to unpleasant side effects in both cases, but the reason behind each condition is different.

When you have an allergy, your immune system becomes overly sensitized to a particular substance. Later on, when you reencounter the allergen, it triggers a harmful immune response in your body. A milk allergy can lead to immediate symptoms such as sneezing, itchy nose, watery or swollen eyes, hives, wheezing and anaphylaxis, a severe and potentially life-threatening condition that can prevent you from breathing properly. In contrast, lactose intolerance is not caused by your immune system. It's caused by a lack of an important enzyme found in the gastrointestinal system.

Many milk products contain a sugar called lactose. In lactose intolerance, your body does not make enough lactase, an enzyme that breaks down lactose into simpler sugars that the body can use—glucose and galactose.

If people are unable to break down lactose in their intestinal tract, their bodies can't absorb it. The lactose travels through their small intestine and ends up in the colon, where it's absorbed by gut bacteria that live in the digestive system. As the gut bacteria break down lactose, they release fatty acids and gases, like carbon dioxide, hydrogen and methane. These gases are what cause nausea, vomiting, stomach cramps and bloating. Unlike symptoms of milk allergy, which can occur immediately after consuming products that contain milk, symptoms of lactose intolerance may take time to develop.

You can manage lactose intolerance the same way you'd manage dairy allergies—by avoiding foods that contain milk. However, some people can avoid the symptoms of lactose intolerance by taking over-the-counter lactase supplements when they eat foods that contain dairy, or by limiting the amount of lactose in their diet. Lactase supplements help to break down lactose and allow the body to absorb the glucose and galactose.

Your healthcare provider can distinguish between lactose intolerance and a milk allergy by ordering a specific set of diagnostic tests. To identify lactose intolerance, your provider may order a hydrogen breath test and a lactose tolerance blood glucose test. A doctor specializing in allergies may order a prick test to test for milk allergies. If you think you have lactose intolerance, you can talk with your healthcare provider to review your history, triggers and symptoms.

Updated by Julie McDaniel, MSN, RN, CRNI, August 2024.