Increase Absolute Humidity Indoors

Indoor temperature, humidity, and ventilation must be increased in public and private buildings to curb COVID-19 transmission. Indoor temperatures of above 75°F (24°C) and relative humidity levels of 50%-60% are recommended.

Good ventilation (rapid exchange of indoor and outdoor air) also decreases the coronavirus spread. 

A large body of research shows that low temperatures and low humidity contribute to flu-like virus epidemics, while high temperatures and high humidity reduce or even prevent flu-like epidemics. The results are confirmed in the lab. COVID-19 is caused by a coronavirus SARS-CoV-2. Coronaviruses and Influenza viruses are enveloped RNA viruses from the respiratory virus group, so this knowledge is fully applicable to the current epidemic. There are many mechanisms by which higher absolute humidity suppresses these viruses, including:

  • keeping our mucous membranes wet and better capable of dealing with the viruses
  • faster virus deactivation on surfaces and in the air
  • decreasing amount of virus which is expelled with cough in droplets but remains in the air as aerosol

People in the US and other developed countries spend most of their time indoors. The typical indoor conditions are characterized by very low relative humidity, lower than optimal temperature, and bad ventilation. Heating and air-conditioning without humidification dries indoor air, and the low humidity contributes to survival, infectivity preservation, and transmission of the coronavirus. There is evidence that the indoor climate has been worsening over the last 10-15 years.

Don’t turn on A/C for as long as possible. Keep windows open.

See Increased indoor humidity may decrease #Coronavirus #COVID-19 transmission in WUWT for the full article with annotated references.

From the draft, March 19:

Medical Sources:

How humidity could help fight coronavirus
Humidity could be helpful in relieving the symptoms of coronavirus, as well as preventing it from spreading

Study: Humidifiers May Help Fight Flu
The finding also suggests that using a humidifier may be a good idea in places where the spread of influenza poses a serious threat …

High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs [found on]

Modeling the airborne survival of influenza virus in a residential setting: the impacts of home humidification

Laboratory research studies indicate that aerosolized influenza viruses survive for longer periods at low relative humidity (RH) conditions. Further analysis has shown that absolute humidity (AH) may be an improved predictor of virus survival in the environment. Maintaining airborne moisture levels that reduce survival of the virus in the air and on surfaces could be another tool for managing public health risks of influenza.

General Media:

Humidity helps in the fight against COVID-19, virologists report

low ambient humidity hurts the ability of the immune system to fight respiratory viral infection

Consumer Reports recommends humidifiers to decrease flu-like virus transmission.


By raising indoor relative humidity levels to 43 percent or above [here, 75% is recommended], investigators reported that they were able to quickly render 86 percent of airborne virus particles powerless.

Maintaining indoor relative humidity >40% will significantly reduce the infectivity of aerosolized virus.

Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature

Previous studies indicate that relative humidity (RH) affects both influenza virus transmission (IVT) and influenza virus survival (IVS). Here, we reanalyze these data to explore the effects of absolute humidity on IVT and IVS. We find that absolute humidity (AH) constrains both transmission efficiency and IVS much more significantly than RH.

CDC: Common Human Coronaviruses

Not specific to COVID-19.

There is no vaccine to protect you against human coronaviruses and there are no specific treatments for illnesses caused by human coronaviruses. Most people with common human coronavirus illness will recover on their own. However, to relieve your symptoms you can:

    • take pain and fever medications (Caution: do not give aspirin to children)
    • use a room humidifier or take a hot shower to help ease
    • a sore throat and cough
    • drink plenty of liquids
    • stay home and rest

If you are concerned about your symptoms, contact your healthcare provider.

“germs may be able to survive in the drier air conditions. So the thought is that, if you keep the humidity level up in a room, the virus is less likely to survive.”

“influenza virus transmission and stability, have identified absolute humidity and temperature as climatic predictors of influenza epidemics in temperate regions of the world”

“Breathing dry air can cause respiratory ailments such as asthma, bronchitis, sinusitis and nosebleeds. “The mucus that normally should be gooey and thick and can trap infection gets drier. So you’re more likely to get a cold because your mucus is not as able to catch things that you breathe in.”

Notice that this study was done on SARS-CoV, NOT on SARS-CoV2, the COVID-19 virus.

In this study, we showed that high temperature at high relative humidity has a synergistic effect on inactivation of SARS CoV viability while lower temperatures and low humidity support prolonged survival of virus on contaminated surfaces. The environmental conditions of countries such as Malaysia, Indonesia, and Thailand are thus not conducive to the prolonged survival of the virus. In countries such as Singapore and Hong Kong where there is a intensive use of air-conditioning, transmission largely occurred in well-air-conditioned environments such as hospitals or hotels.

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