Causes of Lactose Intolerance

In most cases, lactose intolerance develops slowly over time. In many people, the body begins to produce less lactase beginning around two years old. As these people become older, they lose the ability to produce lactase, but symptoms of lactose intolerance may not appear until well after childhood. No one knows why this occurs. In other cases, certain digestive diseases or injuries to the small intestine can cause lactose intolerance. Both can reduce the amount of lactase produced by the lining of the small intestine. Another very rare cause is being born without the ability to produce lactase.