Relative humidity
According to previous studies, major indoor environmental factors influencing bioaerosol concentration include relative humidity, characteristics of air ventilation systems, seasonal variation, temperature, and chemical composition of the air. Other factors, such as the type of home, building material, geographical factors, do not seem to have significant impacts on respirable fungi and bacteria (important constituents of bioaerosols). Relative humidity is one of the most widely studied influencing factors for indoor bioaerosols. Concentrations of two categories of bioaerosols, endotoxin and airborne fungi, are both positively related to indoor relative humidity (higher concentration associated with higher relative humidity). Relative humidity also affects the infectivity of airborne viruses. Regarding the characterisation of air ventilation system, increased use of central air conditioning is found to be associated with lower fungal bioaerosol concentration.