Lactose intolerance happens when your body can't properly digest lactose, a sugar found in dairy products like milk, cheese, and ice cream. An enzyme called "lactase" usually breaks down lactose in your small intestine, allowing your body to absorb it. When you lack sufficient lactase, the undigested lactose travels to your colon, where it's digested by bacteria, leading to symptoms such as gas, bloating, diarrhea, and abdominal discomfort. While some people maintain sufficient lactase levels their whole lives, others might develop lactose intolerance.