The U.S. Food and Drug Administration offers strict guidelines in regard to milk storage. According to these guidelines, milk requires refrigeration at or below 40 degrees Fahrenheit. If your refrigerator does not come with a thermometer that you can view, the FDA recommends placing a freestanding appliance thermometer inside the refrigerator to help you keep track of the temperature. Do not put milk back in the fridge after it's been left out above 40 degrees for two hours or more. Throw it away.

FDA guidelines are even stricter when it comes to milk left unrefrigerated and exposed to high temperatures. If milk remains in temperatures of 90 degrees Fahrenheit or higher, the FDA says, it will only remain consumable for an hour before growth of dangerous bacteria associated with food borne illness becomes a health risk. After an hour, do not return the milk to the refrigerator -- throw it away.

Pathogenic organisms responsible for food borne illness are common in milk and other dairy products. Keep milk cold by storing it in the preferred temperatures to slow the growth of these pathogens. The FDA warns that outside of the refrigerator, pathogenic organisms double in number every 20 minutes. While healthy adults often recover from exposure to food borne illness, the elderly, pregnant women, young children and people who have weak immune systems may become seriously ill; in some cases, exposure can be life threatening.

The milk you purchase in the supermarket undergoes pasteurization -- the process of heating milk to temperatures high enough to kill pathogens that cause typhoid, tuberculosis and other serious illnesses. It is a misconception by some that in exchange for the removal of harmful pathogens, consumers forsake nutrition. According to the FDA, this is not true. Some consumers opt for unpasteurized milk, which undergoes no treatment to kill pathogens, especially listeria monocytogenes. L. monocytogenes is capable of growing in the refrigerator, exposing the consumer to listeriosis -- a serious illness that can be fatal. While pasteurized milk is the healthier choice, it cannot remain outside the refrigerator longer than FDA guidelines suggest.