Humidity is the measure of moisture in the air. The recommended humidity level for humans is 30% to 50%.

High levels of humidity (most often occurring in warm climates) in the home can cause heat stroke, trigger asthma and create an environment in which dust mites and mold can thrive.

Low levels of humidity (most often occurring in cold climates) in the home can cause dryness in the throat and nose (which dries the mucous membranes and can lead to increased vulnerability to colds and the flu) and can cause allergy and asthma complications.