Lactase Deficiency Definition: Lactase is an enzyme found in the intestines of infants and young children. Most people as with most animals lose the ability to produce this enzyme as they get older. Lactase is an enzyme that breaks down the mild sugar called lactose. As people get older many soon start to notice that every time they drink milk or eat raw milk products they get gas, diarrhea, and or abdominal pain from abdominal cramping. This is caused by the inability to digest lactose. This is common for most people, for most people lose the ability to break down milk by the time they reach adulthood. The elimination of raw milk and raw milk products from one's diet eliminates these symptoms. However, predigested milk products such as cheese and yogart should not be a problem.