Final answer:
Lactase is an enzyme that breaks down lactose into glucose and galactose. It is necessary for the digestion of lactose, which is found in milk. Individuals with lactose intolerance lack sufficient amounts of lactase.
Step-by-step explanation:
Lactase is an enzyme that breaks down the disaccharide lactose into glucose and galactose. This enzyme is necessary for individuals to digest lactose, which is found in milk. For individuals with lactose intolerance, who cannot produce sufficient amounts of lactase, unfermented dairy products can cause digestive issues.