Lactose intolerance, also known as lactase deficiency, is a non-infectious diarrhea caused by low lactase secretion and inability to fully digest and decompose lactose in milk.

Because of the lack of lactose-decomposing enzymes in patients' intestines, lactose can not be digested and absorbed and used by human body. The accumulated lactose will be decomposed into lactic acid by bacteria in the intestine, thus destroying the alkaline environment of the intestine, and making the intestine secrete a large amount of alkaline digestive juice to neutralize lactic acid, so mild diarrhea is prone to occur.

That is to say, lactose intolerance is mainly manifested in gastrointestinal symptoms, such as abdominal tension, bowel sounds, abdominal pain, exhaust and diarrhea.

In addition, whether there is lactose intolerance can be determined by some experiments in clinic. Such as: blood test, breath test, fecal acidity test, intestinal biopsy.

Before the breath test 12 hours, you must fast, and then ingest 50g of lactose diluted with water. If lactose cannot be digested, intestinal bacteria will decompose lactose, produce metabolic changes, and produce hydrogen and methane, which can be detected by a gas chromatograph through the patient's breath. But this experiment will take some time, at least two to three hours.