It's important for bottles to be clean. mimijumi bottles are super easy to clean - just toss them in the dishwasher! The wide mouth means you don't need a special brush to clean them, and the simple design (just 3 parts!) makes clean up quick. That being said, sometimes it's good to get them REALLY clean by sterilizing your bottles. Many people use the microwave to sterilize, but with mimijumi you don't want to.