The duration of lactose intolerance symptoms can vary from person to person. That's because not everyone has the same level of lactase deficiency. Those who are missing a large amount of lactase—an enzyme in the body that breaks down lactose—are likely to experience more intense symptoms than someone with a mild deficiency.

Symptom duration and intensity may also depend on how much lactose-containing foods you ingest. Taking an over-the-counter lactase supplement before consuming lactose-containing products may decrease the severity and duration of symptoms. For this reason, it's difficult to predict with certainty how long each person's symptoms will last.

Symptoms of lactose intolerance typically start 30 minutes to two hours after exposure to a dairy product or other food or drink containing lactose. Once the symptoms begin, they're expected to continue until all the lactose has passed through the intestine and colon. The average time it takes for food to get through the intestines to the colon is 30 to 40 hours. Given this, it might be expected that if no other lactose is eaten, symptoms may last for one to two days after they have started, but this is difficult to predict with certainty. Limiting or avoiding lactose-containing food and drink in the future may help decrease symptom duration.

Fortunately, lactose intolerance symptoms typically improve on their own if lactose is avoided or limited. However, if your symptoms last longer than a few days, discuss this with your healthcare provider so they can help rule out other conditions.

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