Find out about lactose intolerance, including symptoms, how it's diagnosed, treatment and what causes it. Lactose intolerance is an inability to digest lactose, a sugar found in milk and milk products. This condition often runs in families and can affect both children and adults. Lactose intolerance is most common in Asian Americans, African Americans, Mexican Americans and Native Americans. What is lactose intolerance? Lactose intolerance is a common cause of abdominal cramping, bloating, and loose stools. This condition occurs when the body does not have enough of the intestinal enzyme lactase. The job of lactase is to break down lactose, the main sugar in milk. Lactose intolerance symptoms typically hit within 30 minutes to two hours after you’ve had dairy. But undigested lactose can stay in your digestive system for up to two days, leading symptoms to linger. When lactose intolerance symptoms strike, these tips from Dr. Jansson-Knodell may provide relief. 1. Take medications. Lactose intolerance happens when your body can’t produce enough lactase enzyme to break down lactose, a sugar in milk. A large percentage of people worldwide experience this by adulthood. Lactose intolerance is a condition that makes it hard to digest the sugar in milk and milk products, called lactose. People with lactose intolerance often have diarrhea, gas and bloating after eating or drinking foods containing lactose. Millions of Americans can’t digest a certain sugar in milk and milk products called lactose. If you’re one of them, you have lactose intolerance. The condition isn’t harmful, but it can be. Lactose intolerance is most common among people of East Asian descent (with 90% lactose intolerance), people of Jewish descent, people in African and Arab countries, and among some people of Southern European descent. Lactose intolerance is caused by lactose malabsorption, a condition in which your small intestine makes low levels of lactase and can’t digest all the lactose you eat or drink. To diagnose lactose intolerance, your doctor will ask about your symptoms, family and medical history, and eating habits. Lactose intolerance occurs in people who lack the enzyme they need to break down lactose, the sugar in milk. It causes digestive distress when you eat dairy products.