Lactose intolerance, also called lactase deficiency and hypolactasia, is the inability to digest lactose, a sugar found in milk and to a lesser extent milk-derived dairy products. Lactose intolerance happens when the small intestine does not make enough of the enzyme lactase. Lactose intolerance can begin at different times in life. In Caucasians, it usually affects children older than age five. In African Americans, lactose intolerance often occurs as early as age two. Symptoms include: Abdominal bloating, abdominal cramps, diarrhoea, gas (flatulence), nausea. Infants or children may have slow growth or weight loss.