Not only can it burn them, it also can take some of the nutriton out of the milk. Besides microwaving is kind of an old way to do it and so is putting it in boiling water. I am going to get the bottle warmer from walmart. They have two of the that look alike except one of them has a little coller on the back that can hold two bottles, and it can keep them cool for 8 hours. Oh and it is portable. I am also going to get a little coller that looks like a lunch bag, that is supposed to keep the bottles cool too, but the only reason I am getting that is b/c if comes with a car bottle warmer that you plug into the car lighter. Any way both of them are made so the bottles can't overheat.