Milk allergy
Lactose intolerance

Milk allergy is distinct from lactose intolerance, which is a nonallergic food sensitivity caused by the lack of the enzyme lactase in the small intestines to break lactose down into glucose and galactose. The unabsorbed lactose reaches the large intestine, where resident bacteria use it for fuel, releasing hydrogen, carbon dioxide and methane gases. These gases are the cause of abdominal pain and other symptoms. Lactose intolerance does not cause damage to the gastrointestinal tract. There are four types: primary, secondary, developmental and congenital. Primary lactose intolerance is caused by decreasing levels of lactase brought on by age. Secondary lactose intolerance results from injury to the small intestine, such as from infection, celiac disease, inflammatory bowel disease or other diseases. Developmental lactose intolerance may occur in premature babies and usually improves over a short period of time. Congenital lactose intolerance is an extremely rare genetic disorder in which little or no lactase is produced from birth.
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