People who are lactose intolerant are missing the enzyme lactase, which breaks down lactose, a sugar found in milk and dairy products. Undigested lactose ferments in the intestine producing gas, bloating, diarrhea, nausea, and cramps. While lactose intolerance can cause great discomfort, it is not life-threatening. Some people with lactose intolerance can digest yogurt and other cultured milk products because the lactose is digested by the bacteria in the fermented food. Sometimes people can still generate small amounts of lactase themselves and may be able to tolerate some dairy products but not others.