A humidifier is a device that blows cool to lukewarm mist (vapour) into the air to increase humidity (moisture) in a room. A vaporizer is a device that releases a cool to hot mist into the air to help increase humidity or to help with breathing.

These devices tend to be used when a person is sick or when air in the house is dry (low indoor humidity). When a person's skin and mucous membranes are dry, the dryness can aggravate an illness of the head, neck, or chest. Or it can lead to chapped lips, a dry throat, or dry and itchy skin. Mist therapy with one of the devices can help provide relief.

These devices differ in a few ways.

• A steam vaporizer boils water and releases steam into the air. The steam is germ-free, but the hot water can burn anyone who overturns or gets too close to the device.
• Evaporative (wick) humidifiers use a filtered wick to absorb water. A fan blows air through the moist wick, releasing a cool-to-lukewarm mist. Some models can sense when the air in the room is dry and turn themselves on and off to control humidity. Because the water in a humidifier isn't boiled, bacteria, mould, and minerals (dust) can be in the mist. Using distilled water and carefully following the safety instructions can help keep the mist clean and safe. Depending on the model of the humidifier, a person may need to empty the water on a regular basis. Some humidifier models are quieter than others.