Water vapor or humidity is usually not considered an air contaminant or cause of health problems. Yet, studies show that when indoor humidity levels are out of range, it can have a detrimental impact on building occupants. Many experience adverse reactions and, long term can lead to illness. This post discusses how humidity can easily compromise health and comfort. With the proper cooling systems in place, balanced humidity levels can be achieved, which will allow for healthier and happier occupants.


Poor humidity directly affects comfort. Upon exposure to very low or very high humidity levels, one can experience:

  • Eye and skin irritation
  • Static electricity
  • Thermal discomfort

A September 2017 article from the ASHRAE Journal sourced data from studies conducted. The data found that when low humidity levels are present eye and skin irritation appear. In fact, eyes were drier with a relative humidity (RH) of 5% compared to a RH at 35%.  Similarly, it was noted that an individual’s skin suffered an increased water loss at lower humidity levels. Mild skin discomfort was observed <30% RH. The Journal also noted that there was increased static electricity at and below 20%–30% RH.

In an issue of Environmental Health Perspectives, it was noted that relative humidity has an adverse effect on thermal discomfort when high humidity is combined with high temperatures. The combination can cause great discomfort and lead to exhaustion, heat stroke, or fatal illnesses.


Many biological contaminants (bacteria, fungi) and pathogens can have a severe impact on health when the humidity levels are not balanced. Studies illustrate health is impacted after prolonged exposure to low or high humidity levels, and one can experience allergies, asthma, and long-term illness.


Two major causes of allergies indoors are dust mites and fungi. Both thrive in high humidity. In the ASHRAE Journal article, low humidity at <60% RH was shown to be beneficial for reducing both allergens. However, asthma has been shown to be exacerbated when there is very low humidity.


Airborne pathogens that cause bacterial infections and viruses are a growing concern, particularly within office environments. Studies noted in the ASHRAE article tested influenza within a wide range of humidity levels. Influenza survival experienced a significant dip between 40% and 80%.

Balancing humidity levels with the proper cooling system

One can infer from the information presented that properly balanced humidity levels could be in the mid-range. Some conclude that balanced humidity is a range of 30–60% RH while others suggest 40–80%. The sad news is there is not a magic right number, as it depends on variables such as conditions, construction, climate, and location.

Building design has evolved over the years to withstand higher relative humidity levels, but if the building doesn’t include a proper cooling system there is no guarantee that humidity levels won’t spike or plummet. Modern cooling systems are able to monitor the air quality, respond to external weather conditions, and adapt their cooling strategy without compromising performance or the building owner’s pocketbook.

Learn how Air2O cools and adds modest moisture to the supply air stream to maintain the most healthy humidity levels available.