While drinking spoiled milk is unlikely to be lethal for an otherwise healthy adult, it may cause food poisoning. For children and those people with vulnerable immune systems, this could be severely problematic. Drinking spoiled milk is associated with the risk of staph food poisoning, or infection by Staphylococcus aureus, particularly when the milk has not been stored at a low enough temperature.
Staph food poisoning can be avoided in milk and other dairy products by storing them at temperatures lower than 40 degrees Fahrenheit. Milk should be refrigerated shortly after purchase in order to maintain a fairly stable temperature. For the same reason, it is best not to return unconsumed milk to the original container if it has been at room temperature for a period of time.
Typically, it can be determined whether milk has spoiled based on its smell. If it does not smell unpleasant, it is likely safe to drink. The expiration date on the label is not a reliable indicator of spoilage, but milk will not generally keep for longer than a few days after this date.
Symptoms of staph food poisoning include nausea and vomiting, stomachaches and diarrhea. It may also be accompanied by dehydration and the associated symptoms of headache, muscle cramps and increased heart rate.