Nearly 600 papers were reviewed regarding the effects of humidity on comfort, health, and indoor environmental quality (IEQ), of which 70 focused on low humidity (RH40%) and were thoroughly analyzed. Low humidity had little effect on thermal comfort, but increased skin dryness, eye irritation, and static electricity. Low humidity increased the survival of some pathogens, e.g. influenza. Low humidity showed non-uniform effects on volatile organic compound emissions and indoor air quality. Temperature, ventilation rates and time were noted as confounding variables. Most studies with adults utilized exposure times of maximum three hours; few studies used children, adolescents or elderly subjects.

Today, humidification is used primarily to protect materials and aid in manufacturing processes. However, data tells us that proper air hydration is also essential for our health. People resist short term dehydration by thirst-prompted (dry mouth) fluid intake. Conversely, chronic dehydration from water evaporation through skin and respiratory tissues in dry indoor air is unperceivable, yet has dire health consequences. Dry indoor air decreases our resistance to infections and allergies while providing a perfect environment to enhance microorganisms' infectivity and dissemination. This seminar presents new and existing data on the health benefits of proper air humidification.

ASHRAE research project “Limiting criteria for human exposure to low humidity” was conducted in 2001-2002 at the Technical University of Denmark. The impact of humidity on comfort and working performance was measured subjectively and objectively at 5%rh, 15%rh, 25%rh and 35%rh at 22°C (71.6°F) and at 18°C, 22°C and 26°C at 2.4 g/kg. The effect of low humidity was observed at both clean and polluted indoor environment. The results found that low humidity had negative impact on mucous quality and working performance that requires visual attention. Some interactions between low humidity and air pollution on dryness symptoms were observed.