A humidifier is a small appliance that changes water into steam in order to increase the moisture level in the air. Humidifiers come in "cool mist" and "warm mist" varieties. Without regular cleaning, mold and bacteria can grow in the unit and cause a foul odor. Regular maintenance of a humidifier must include changing the filter and cleaning the water reservoir.
Empty the reservoir or tank of the humidifier every day. Wipe it dry with a clean towel and refill it with distilled water. Distilled water lacks the minerals found in most tap waters, which can encourage the growth of bacteria.
Wipe down the tank once every three days with hydrogen peroxide when you change the humidifier's water. Soak a clean sponge with the hydrogen peroxide and wipe the entire surface of the tank, inside and out.
Rinse the tank in tap water and dry it with a clean towel.
Replace the humidifier filter according to the manufacturer's instructions. The frequency with which you need to change the filter and the method for doing so will vary with your humidifier model.
Keep the humidifier on a flat, stable surface, away from any fabrics. Keep the area around the humidifier dry.