Bad milk contains bacteria that is capable of causing illness upon drinking it. According to KidsHealth, bacteria from milk, such as salmonella, causes nausea, diarrhea and vomiting.
In most cases, food poisoning from milk and other foods resolves itself without hospitalization, KidsHealth reports. People with food poisoning should strive to stay hydrated while their bodies expel the illness.
The Dairy Council of California reports that it is a myth that once the date on a milk container expires, it is no longer safe to drink. That date is the sell-by date, not the use-by date. As long as the milk remains fresh to taste and smell, it is considered safe to drink.