Drinking spoiled milk can cause digestive distress, such as vomiting, abdominal cramping, and diarrhea. The symptoms can occur several hours or even several days after drinking spoiled milk. The reason why spoiled milk can be harmful is due to the bacteria found within it. Spoiled milk is the result of an overgrowth of bacteria that compromises the texture, flavor, and overall quality of milk. Milk naturally contains bacteria that can spoil and cause diseases, such as Escherichia coli and Salmonella. Drinking small quantities of spoiled milk can cause no symptoms or some minor symptoms, which will typically go away on their own. However, drinking larger amounts of spoiled milk can cause stomach distress resulting in abdominal cramping, vomiting, and diarrhea, similar to a food-borne illness.

It is best to avoid drinking spoiled milk in large or even moderate quantities. If you accidentally ingest a small sip of spoiled milk, you don’t need to worry, but it is still not a good idea to drink it. If your milk is very old and has started to curdle, become slimy, or grow mold, it’s best to throw it out.