Why can't you digest sugar in milk if you are lactose intolerant?

Lactose intolerance occurs when the body lacks sufficient levels of lactase, the enzyme needed to break down lactose, the sugar found in milk. Without enough lactase, lactose remains undigested in the intestines, leading to symptoms like bloating, gas, and diarrhea when dairy products are consumed. This inability to properly digest lactose is what characterizes lactose intolerance.