There are several types of humidifiers available, including evaporative humidifiers, ultrasonic humidifiers, and steam humidifiers. Evaporative humidifiers are the most common type and work by blowing air over a wet wick or filter. They are relatively inexpensive and easy to maintain but can be noisy and produce a white dust. Ultrasonic humidifiers use high-frequency sound waves to create a fine mist and are quieter and more energy-efficient than evaporative humidifiers. Steam humidifiers use electricity to heat water and produce steam, which is then released into the air. They are often more expensive than other types but can be more effective in very dry environments.