Lactose intolerance is more common in certain countries and ethnic groups. It's common in places where milk isn't part of the usual adult diet e. g. in South America, Africa and Asia more than half of people have lactose intolerance. Sometimes you can have lactose intolerance temporarily because the lining of your small bowel(where lactase is produced) has been damaged. This is called secondary lactose intolerance.
Attribution: BUPA