Lactose intolerance is a disorder in which a person is not able to digest lactose, a natural sugar found in milk-based foods, such as ice cream. People with lactose intolerance do not have enough lactase in the small intestine to properly digest lactose, so it passes through to the large intestine, where it causes gas, pain in the belly, and bloating.

Some people have lactose intolerance from an early age, while others develop it later in life. An intestinal illness may sometimes cause a person to be unable to digest lactose for a short time.

There is no cure for lactose intolerance. However, the symptoms of lactose intolerance can be treated by reducing (or avoiding) milk and dairy products, using dietary supplements called lactase products that help digest lactose, or using special food products that contain reduced amounts of lactose. Because milk and dairy products are important sources of calcium, people with lactose intolerance need to be sure to get enough calcium from other sources.