Every breastfeeding mother who pumps has to be extra cautious about the "shelf-life" of her breastmilk. Like every other food, expressed breast milk can go bad, making it unsafe for your baby to drink. But just how quickly does breast milk go bad? That depends greatly on how and where you store it once you've pumped. Unlike formula, which has a pretty universal shelf life, breast milk is a bit more temperamental. Luckily, there are guidelines for storing your breast milk so that it stays as fresh as possible for as long as possible.
According to Baby Center, breast milk can sit at room temperature for three to four hours after being pumped. At that point, it's best to use it, refrigerate it or put it in the freezer where it can be stored for a long time.
If you're going on a trip, or just out for the afternoon, your breast milk will last on ice or in an insulated cooler for about 24 hours. If you're not going to use it up within three to four hours, or put it on ice, your milk will last for about five days in the refrigerator, although according to the Mayo Clinic, using it within three is ideal.
Additionally, the Mayo Clinic also noted that breastmilk can be stored in the freezer for up to a year, but using it within six months is ideal, since it can loose many of the nutritional antibodies if its stored for too long.
No matter how you choose to store your milk, knowing that it won't immediately go bad and that you can build up a bit of a stock pile (as long as you're storing it properly) can be a lifesaver for many mothers whether they exclusively pump or pump only as needed.