Children with lactose intolerance don’t have enough of the enzyme needed to digest lactose, the main sugar found in milk and milk products. This enzyme is called lactase, and infants are born with it being made by the lining of their small intestine. For children with lactose intolerance, the amount of lactase in made in intestine decreases over time.
Lactose intolerance is very common. It’s more common among people of Asian, African, Hispanic or Native American descent.
Babies who are born prematurely can have a temporary type of lactose intolerance called developmental lactase deficiency, which lasts only a short time. Another type of temporary lactose intolerance can happen after a child has a gastrointestinal infection. In very rare cases, children are born with a complete lack of lactase because of a genetic defect.