Lactose intolerance is caused by a deficiency of lactase, the enzyme that digests lactose, typically resulting in symptoms such as diarrhea, bloating, and abdominal pain after consuming dairy products. It is relatively common among Chinese people. Unlike lactose allergy, this condition only requires controlling the intake of lactose, rather than completely avoiding dairy products. This disease generally does not present symptoms like passing mucus. The presence of mucus in stool usually suggests the possibility of chronic colitis. In such cases, it is advised to undergo a colonoscopy to examine the intestinal mucosa for mucus attachment, or signs of hyperemia, erosion, or edema.