DefinitionLactose intolerance is the inability to digest lactose (a type of sugar found in milk and other dairy products).Alternative NamesLactase deficiency; Milk intolerance; Disaccharidase deficiency; Dairy product intoleranceCauses, incidence, and risk factorsLactose intolerance happens when the small intestine does not make enough of the enzyme lactase. Babies' bodies make this enzyme so they can digest milk, including breast milk. Before humans became dairy farmers, most people did not continue to drink milk, so their bodies did not make lactase after early childhood.Lactose intolerance is more common in Asian, African, African-American, Native American, and Mediterranean populations than it is among northern and western Europeans.Lactose intolerance can begin at different times in l