Lactose Intolerance Lactose is the primary sugar found in mammalian milk. Digestion of lactose requires the enzyme lactase, produced in the small intestine, which breaks lactose into two simpler sugars. When the intestine produces little or no lactase, milk sugar is not digested. It moves into the colon, where bacteria ferment it, producing hydrogen, carbon dioxide and organic acids.
Newborns require high intestinal lactase levels for survival.
Later in life, though, about two-thirds of all people lose the ability to produce lactase. Types Primary lactose intolerance - may begin at any time but usually develops by early adolescence and continues throughout life. The diseases of the bowel, such as Crohn's disease, can cause lactose intolerance. Congenital lactose intolerance - in which the small intestine produces no lactase. Consumption of any amount of lactose is intolerable and even dangerous, especially for infants, in whom diarrhea quickly leads to dehydration.