Relative Humidity and Its Impact on the Immune System and Infections

Abstract

Relative humidity (RH) represents an underestimated outdoor and indoor environmental parameter. Conditions below and above the optimal range could facilitate infectious transmission as well as the exacerbation of respiratory diseases. The aim of this review is to outline the consequences for health of suboptimal RH in the environment and how to limit this negative impact. RH primarily affects the rheological properties of the mucus, modifying its osmolarity and thus the mucociliary clearance. The integrity of the physical barrier, maintained by mucus and tight junctions, is critical for protection from pathogens or irritants. Moreover, the control of RH seems to be a strategy to prevent and control the spread of viruses and bacteria. However, the imbalance of RH in the outdoor and indoor environments is frequently associated with the presence of other irritants, allergens, and pathogens, and therefore the burden of a single risk factor is not clearly defined in different situations. Nonetheless, RHmay have a synergistic negative effect with these risk factors, and its normalization, if possible, may have a positive impact on a healthier environment.

Extreme temperatures increase the risk of pediatric pneumonia: a systematic review and meta-analysis

“…Exposure to cold caused pediatric pneumonia hospital admissions to increase by approximately 5.1% compared with non-cold exposure (p < 0.05) (40). Dry air during cold events can lead to the drying and irritation of mucous membranes in the respiratory tract, impairing their protective function and facilitating the entry of viruses and bacteria into the airways (41). We observed that extreme cold is an important risk factor for pediatric pneumonia outpatient visits.…”

The Impact of Different Relative Humidity Levels on the Production Performance, Slaughter Performance, and Meat Quality of White Pekin Ducks Aged 4 to 42 Days

“…Relative humidity is, at all temperatures and pressures, defined as the ratio of the water vapor pressure to the saturation water vapor pressure (over water) at the gas tem-perature [62]. The definition of relative humidity makes this environmental parameter difficult to measure and control because it is a ratio rather than an absolute value.…”

Evaluating airflow dynamics in common vertical circulation spaces of a multi-floor apartment building for mitigating airborne infection risks: A CFD modeling study

“…Humidity and carbon dioxide (CO 2 ) play pivotal roles in the design of infection control methods within indoor environments [ 39 ]. Maintaining an optimal relative humidity (RH) is crucial, as studies have shown a significant correlation between humidity levels and infection rates [ [40] , [41] , [42] ]. The role of humidity in reducing infection rates involves a complex interplay of biological and physical factors.…”