Lactase breaks down milk sugar into simpler forms that can then be absorbed into the bloodstream. When there is not enough lactase to digest the amount of lactose consumed, the results, although not usually dangerous, may be very distressing. While not all persons deficient in lactase have symptoms, those who do are considered to be lactose intolerant. Symptoms can include nausea, cramps, bloating, gas, and diarrhea, which begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of symptoms varies depending on the different amount of lactose each individual with this condition can handle.
Lactose intolerance takes several forms.
In a rare condition known as primary lactose intolerance, an infant does not produce any lactose from birth. These infants cannot tolerate breast milk and need to be under the care of a pediatrician and dietitian. The more common type of lactose intolerance occurs after weaning and is known as secondary lactose intolerance. It is quite common. Many people experience transient or episodic lactose intolerance related to well-known digestive conditions.