Spoiled milk can potentially cause food poisoning, resulting in vomiting and diarrhea. The specific symptoms and the severity of the illness depend on which microorganisms colonize the spoiled milk and how much one ingests. In rare cases, bacteria can cause life-threatening illnesses, especially if the milk has been improperly handled.
While most milk available to consumers is pasteurized, it remains safe for only a short while after treatment. Manufacturers use date stamps to identify this safe period and give consumers a guideline on when their products might become unsafe. Improper handling, like leaving milk sit at room temperature, can drastically shorten its safe lifespan.