This is a common disorder arising from an inability to digest lactose (milk sugar) because of low levels of the enzyme lactase. Lactose is the main sugar in milk and milk products from mammals (e.g. humans, cows, goats). Lactose is digested by the enzyme lactase in the small intestine of the gut. If lactase activity is low, undigested lactose passes into the colon (large intestine), where it can cause symptoms of lactose intolerance. Lactose intolerance is often confused with milk allergy, but it is NOT an allergy.
The symptoms of lactose intolerance are:
And less commonly, it can cause constipation and nausea.