Unlike other humidifiers that grow slimy mold and mildew, the pureguardian® 70-Hour Cool Mist Ultrasonic Humidifier uses Silver Clean technology to fight the growth of mold and mildew on the surface of the water tank. Its extended run time eliminates the need to refill the water tank frequently, and thanks to ultrasonic technology it is ultra-quiet when it runs making it ideal to have on while you sleep. The humidifier emits a soothing cool mist, and a low water indicator light lets you know when it's time to refill the water tank. It guards against problems caused by dry air in the home. It makes life pleasant for those with cold, flu, allergies and dry skin.