What is lactose intolerance?

Lactose intolerance is a disorder that occurs when a person cannot digest milk products due to the lack a digestive enzyme called lactase.


Symptoms usually begin about 30 minutes to two hours after having food or beverages that contain lactose. Common symptoms may include:

  • nausea
  • diarrhea
  • cramps
  • bloating or gas


The most common tests for lactose intolerance are:

  • Hydrogen breath test. This test checks the levels of hydrogen on the breath after having a drink that contains lactose. If the levels of hydrogen are high, it may mean that lactose is not being properly digested.
  • Stool acidity test. This test checks the stool for certain acids that form when lactose is not digested.


Many people with lactose intolerance can manage their condition by changing their diet. Some children may need to avoid lactose altogether, while others may be able to limit. Your child’s doctor may also recommend lactase products to help manage symptoms.

Learn more about Pediatric Gastroenterology services at Boston Children’s Health Physicians.

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