Patients with lactose intolerance have high lactase activity at birth, which deteriorations to low levels by adulthood. A lactose-intolerant patient is likely to experience bloating, flatulence, and abdominal pain after drinking milk products. This response happens due to the lack or deficiency of the enzyme lactase, which is obligatory for the absorption of the carbohydrate lactose. Pyrosis, or heartburn, is a burning sensation in the esophagus and stomach due to the reflux of gastric acid. It is not produced by lactose intolerance. Common reasons of constipation contain decreased physical activity, a low-fiber regimen, insufficient consumption of water, and certain medicines. Lactose intolerance is not the source of constipation.