Humidifiers may be in various sizes and shapes, ranging from hatbox-sized portable humidifiers to furniture-sized units.  However, they have the same function: they place moisture in the air. And they may do it in five absolutely different ways.
1. Evaporation
Evaporative humidifiers contain a fan inside, which drives air through a wet pad and then that dampened air comes into the room.
Evaporative humidifiers don’t create a spray and, as a result, are less prone to distribute various bacteria than are humidifiers that put a cool mist into the air. However, the wet pads may become a favorable ground for different microbes if not cleared recurrently.
2. Steam
This type of humidifiers, frequently called vaporizer, boils water and puts it into the air as steam. They are not likely to throw bacteria into the air; in any case, it would be extremely difficult for any germ to stay alive after the boiling process.
On the contrary to other types of humidifiers, they create very little or no “white dust.” Steam humidifiers get rid of the mineral substances while boiling water in their tanks.
3. Warm Mist
These humidifiers operate almost the same as steam vaporizers. They boil water, however, the steam is a little cooled prior to leaving the unit in the form of a mist of warm water drops as a substitute to real steam.
4. Cool Mist
Such humidifiers disintegrate water into minute drops and throw a cool mist into the air. As the water is not boiled, the chilly spray can enclose potentially dangerous bacteria in case the tank is not appropriately cleared and disinfected.
5. Ultrasonic
That kind of humidifiers makes use of high-frequency vibrations to disintegrate water drops into enormously tiny mist. The spray created by these humidifiers comprises no molds and relatively few live microorganisms. It is considered that the ultrasonic vibrations can disintegrate and destroy microorganisms together
with the water drops.
Nevertheless, even if these parts of lifeless bacteria can cause no infections, they can still arouse allergic reactions in people susceptible to them.
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