Lactose intolerance means you have trouble digesting lactose. Lactose is the sugar found in milk and foods made with milk. The small intestine needs lactase enzyme to break down lactose. With lactose intolerance, you may not feel well when you eat or drink something with lactose because you don't have enough lactase enzyme. Many people have problems digesting lactose. Some people become lactose intolerant as children. In others, the problem starts...