A condition caused by a lack of an enzyme called lactase, which, in turn, causes the body to be unable to digest lactose, a sugar found in milk products. Common symptoms, which begin about 30 minutes to two hours after consuming foods or beverages containing lactose, may include: nausea, cramps, bloating, gas and/or diarrhea. The severity of symptoms varies depending on the amount of lactose consumed and the amount that an individual can tolerate.