Lactose intolerance is a condition in which the body is unable to fully digest lactose, a form of natural sugar found in milk. Lactose intolerance is not the same thing as a food allergy and is a relatively common condition. It is more common in Native Americans and people of Asian, African, and South American descent than among people of European ancestry. The condition results from a deficiency of lactase, an enzyme made in the small intestine that breaks down lactose. Symptoms occur when an affected person consumes milk or dairy products. Symptoms can include abdominal pain, bloating, vomiting (throwing up), diarrhea, and gas. The degree or severity of symptoms can vary among affected people.