Many manufacturers claim that their humidifiers are antimicrobial, but this really depends on the type of humidifier they are selling. Most ultrasonic humidifiers and vaporizers emit some bacteria while you’re using them, while evaporative models do not. To ensure no bacteria is coming out of your humidifier along with the mist, the best thing to do to dump the excess water out daily and clean it at least once a week. Also, be sure it is completely dry when you are not using it to prevent mold or mildew.