Whether overnight milk can be consumed depends on whether the container is in an airtight state, whether the temperature is suitable for preservation, or whether the milk has come into contact with oral secretions and bacteria.
If the container in which the overnight milk is stored is in an airtight condition and it is placed in the refrigerator for chilling, after taking it out on the next day, if it is observed that there is no change in the appearance, odor or taste of the milk, it is generally acceptable to reheat it and drink it.
If the milk has already been consumed, or has been stored at room temperature for too long, it is not recommended to drink it after overnight. Because the human mouth contains bacteria, direct or indirect contact with the milk will lead to bacteria leaching into the milk. And milk is rich in nutrients, creating a good environment for bacteria to survive and reproduce. If milk is contaminated and spoiled by bacteria, drinking it may cause abdominal pain, diarrhea and other digestive symptoms.
It is recommended to consume milk on a daily basis as needed and keep it reasonably preserved to avoid discomfort caused by drinking spoiled milk.