Indirect health effects of relative humidity in indoor environments.

Abstract

A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused bLy relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens.

Scottish Passive House: Insights into Environmental Conditions in Monitored Passive Houses

“…The optimal parameters of RH for health are defined by Arundel et al as 40%-60% humidity; beyond this range, RH can impact on respiratory infections and allergies, by reducing the infectivity of airborne-transmitted infectious bacteria and viruses [44]. In Passive House design, the RH optimal comfort range is 35%-55%, for the avoidance of "mould and the fast growth of HDM" [19] (p. 6).…”

Odors and Sensations of Humidity and Dryness in Relation to Sick Building Syndrome and Home Environment in Chongqing, China

“…Chamber experiments using clean air showed no drying out of the mucosa after exposure to 9% relative humidity for 78 hours [30]. However, Green [31] and Arundel [32] found that dry indoor air could impair the ciliary function, resulting in an increased occurrence of respiratory infections. RH about 40% has been suggested to be better for the eyes and the airways than levels below 30% [33].…”

The ignored diversity: complex bacterial communities in intensive care units revealed by 16S pyrosequencing

“…Indoor microbial communities are an important component of everyday human health37, and are even partially composed of human-associated bacteria1 due to the high emission rate of up to 10 6 bacteria per person-hour8. In ICUs, sanitation protocols are stricter than in other areas of the hospital, yet many patients treated in ICUs are infected with hospital-acquired “nosocomial infections” often due to an underlying severe disease910.…”