Lactose intolerance is a food intolerance that occurs after ingestion of lactose. To digest lactose, the body needs an enzyme called lactase. Lactose intolerance occurs when the small intestine does not produce enough lactase. To diagnose this intolerance can be performed three medical tests: Lactose-hydrogen breath test, lactose tolerance and pH of feces. The only treatment for lactose intolerance is to reduce or avoid your intake.