It’s not necessary. Bottles need to be sterilized before their first use, since you can’t know where they’ve been and who has handled them before purchase. After that, a good washing should do the trick. You may wish to sterilize them again periodically, especially after your child has been sick. The Center for Disease Control says you can stop sterilizing when your baby is three months old because by that point, a baby’s immune system has developed sufficiently to offer protection against common germs. Many dishwashers include a sterilizing setting, and many baby brands sell microwave or countertop sterilizers. The easiest way, however, is to boil the bottles in a pot on the stovetop for five minutes.