Symptoms of lactose intolerance mainly include gastrointestinal symptoms such as abdominal pain, diarrhea, nausea, vomiting, hyperactive bowel sounds, and excessive gas. The reason for lactose intolerance has a lot to do with the patient’s gastrointestinal digestive ability. Some patients have an inborn deficiency of the enzyme lactase, which can lead to the patient’s intolerance to lactose. However, normal people can also suffer from various digestive diseases that damage the gastrointestinal mucosa and can also develop symptoms of lactose intolerance. When a lactose intolerant patient drinks milk or other dairy products, lactose enters the intestines, and because the patient’s intestines cannot secrete lactase or secrete less lactase, the lactose cannot be digested and absorbed. The undigested lactose will be broken down into lactic acid by bacteria in the intestines, which will destroy the alkaline environment in the intestines. In order to neutralize this lactic acid, the intestines will secrete a large amount of digestive juices, which will lead to diarrhea, abdominal pain, and hyperactive intestinal sounds, and other symptoms. A large amount of gas is also produced during the bacterial decomposition of lactose, which can lead to symptoms of bloating and increased gas.