We only use 4 ounces of formula a day, for cereal. The cans say that you have to use them within a month of opening. What happens if they hang around for longer than that? I can't finish a small can in a month, but I also have a second can that was opened because we had a crisis when we were out of town. It has been opened for 2 months now. Am I going to poison my kid if I give it to him anyway? I'm thinking it would probably be OK but I'm just wondering if anyone knows the real reason behind the one month limit.