What is relative humidity?

Relative humidity is a ratio of the amount of water vapor currently in the air compared to the amount of water vapor the air could theoretically hold at that given temperature.

For example, 40% relative humidity, means that the air is holding 40% of the water vapor it could hold at that temperature.

Why does relative humidity matter?

Humans sweat to keep cool.

If the relative humidity for an 80-degree day is 100%, then your sweat will not evaporate into the air because the air is at its saturation limit.

If the relative humidity is at 25%, then the air is dry and pulls moisture from your skin, nose, lips, and mouth. This can result in bloody noses, dry throats, dry mouth, and dry skin.

Humans are most comfortable between 40-60% relative humidity.

How does relative humidity impact airborne viruses?

Airborne viruses travel through infected aerosols of tiny water droplets. A person expels aerosols through talking, breathing, singing, laughing, sneezing, coughing, etc. These aerosols will change size depending on the amount of humidity in the air.

In lower humidity, aerosols shrink, making it easier for the virus to get into the body and infect the person. These smaller aerosols weigh less and are picked up in airstreams allowing them to travel farther and longer increasing their rate of infection. 

In high humidity, aerosols are larger, heavier, and fall to the ground quicker than their counterparts. Once they fall to the ground, they are still able to infect people. Excess moisture is uncomfortable and inhabitable for humans.

By keeping your home in the Healthy Humidity range (between 40-60%), you’re providing enough moisture to keep your body’s immune response high and enlarging the virus enough to lower its infection rate.

How do I know that my house has the proper humidity?

If your skin is dry, you have a scratchy throat, and you are getting bloody noses, then the air is likely too dry. Dry air can also crack your wooden furnishings.

In moist air, you’re likely also very miserable. You probably have mold or mildew growth, feel clammy, and may even have a pest infestation. One of the best indicators that the air is too moist, is if the air has a mildew smell.

Relative Humidity Solutions

AprilAire Humidifier | AprilAire Dehumidifier | AprilAire Healthy Air System

Relative Humidity Resources:

EPA - https://www.epa.gov/mold/mold-course-chapter-2

CDC - https://www.cdc.gov/niosh/topics/indoorenv/temperature.html

ASHRAE - https://www.ashrae.org/file%20library/technical%20resources/covid-19/i-p_s16_ch22humidifiers.pdf