The best humidifier to use for essential oils is an ultrasonic humidifier. This is because if the oil is added to an evaporative humidifier, it could be trapped by the wicking filter, causing it to break down and possibly fail. A safe alternative is an ultrasonic humidifier, which does not contain a filter and instead uses high-frequency vibrations to emit the oil mist. This will give you more assurance that you can enjoy the health and aromatic benefits of essential oils without worrying that the humidifier could break down.