Definition - What does Relative Humidity mean?
Relative humidity is a measurement of the amount of moisture in the air expressed as a percentage of saturation point at any given temperature. Various electronic sensors and equipment can be used to measure relative humidity with a greater or lesser degree of accuracy. In the context of occupational health and safety, relative humidity is of importance in air-quality measurements. OSHA recommends that indoor humidity should be within a range of 20 - 60%.
Safeopedia explains Relative Humidity
High humidity causes physical discomfort and promotes the growth of mold and microorganisms that can trigger allergies. Overly low humidity causes irritation of the respiratory system and dry, itchy eyes. It is therefore an important measure of the air quality to which sedentary workers are exposed and may have significant health implications in the long term. Health and safety professionals are required to monitor various aspects of indoor air quality including relative humidity. Temperature also affects relative humidity. The colder the air, the less moisture it can hold and the higher the relative humidity will be.