A humidifier is a device that adds moisture to the air in a room or other enclosed space. It is typically used to increase the level of humidity in a room to make it more comfortable for occupants, or to help prevent the growth of mold and mildew. Humidifiers come in a variety of sizes and types, including evaporative, ultrasonic, and steam. Evaporative humidifiers use a fan to draw air through a wet filter, while ultrasonic humidifiers use ultrasonic vibrations to create a fine mist. Steam humidifiers boil water to create steam, which is then released into the air. All types of humidifiers can help improve air quality, reduce static electricity, and help relieve dry skin and other respiratory symptoms.