Common symptoms include nausea, cramps, bloating, gas, and diarrhea, which begin about 30 minutes to two hours after eating or drinking foods containing lactose. The severity of symptoms varies depending on the amount of lactose each child can tolerate.
In rare cases, children are born without the ability to produce lactase. For most children, however, lactase deficiency is a condition that develops naturally over time. After about the age of two, the body begins to produce less lactase, but many people may not experience symptoms until they are much older.
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