What Causes Diarrhea After Drinking Plain Milk?

Most people choose to drink plain cow’s milk to supplement calcium in daily life. However, some individuals experience significant discomfort after consuming milk—particularly diarrhea. What causes diarrhea following the consumption of plain cow’s milk?

What Causes Diarrhea After Drinking Plain Cow’s Milk?

Lactose intolerance is the primary cause of diarrhea after drinking plain cow’s milk. Insufficient lactase enzyme secretion in the small intestine impairs the digestion and absorption of lactose present in milk, leading to increased osmotic pressure within the intestinal lumen and resulting in diarrhea. Secondly, a milk allergy may be responsible. Some individuals are allergic to certain proteins in milk; upon ingestion, an allergic reaction occurs, manifesting as diarrhea. Lastly, diarrhea may result from consuming contaminated or excessively cold milk—especially in individuals with compromised gastrointestinal function, as the gastrointestinal tract becomes irritated and reacts accordingly.

Lactose intolerance is classified into two types: primary (congenital) and secondary. For example, some patients recovering from gastroenteritis may develop diarrhea upon drinking milk immediately after recovery; however, this symptom often gradually diminishes or even resolves over time. Gradually increasing milk intake in small increments allows the gut to adapt progressively, thereby reducing lactose intolerance symptoms. Conversely, some individuals have had lifelong intolerance to milk due to congenital lactase deficiency. Such individuals are advised to avoid dairy products altogether.

Lactose-free milk is now commercially available. Patients experiencing severe diarrhea may opt for this alternative. We hope this information proves helpful.