Humidity and the COVID-19 Virus – Update

Written by Gil Durrant October 8, 2021 0 comment

Humidity and the Covid-19 Virus

Humidity and the COVID-19 Virus – Update

Winter is Coming

This is a Humidity and the Covid-19 Virus – Update in preparation for  winter. Reports have shown that breathing air which is below recommended humidity levels irritates respiratory passages and contributes to a heightened risk of COVID-19 and influenza.

A side affect of social distancing is a reduction to the day to day challenges from viruses your body normally experiences.  Your body has not had to fight infections and develop immunity and the common cold may result in a more severe infection and a longer recuperation period.

The Evidence for the Link Between Humidity and Transmission

As per our previous blog a report in the Transboundary and Emerging Disease Journal raises the link between humidity and the Covid-19 virus. It suggests there is a link between relative humidity and an increase in community transmission. with an increase of 7 to 8% in COVID-19 cases for every 1% drop in relative humidity.

What is relative humidity?

Relative humidity is the amount of water vapour in the air compared to the total amount of water vapour the air can hold. Relative humidity decreases with the use of heaters as they increase the air’s capacity to hold water. This causes the relative humidity to drop drastically.

Many people develop a dry throat and an irritating cough in winter due to this dry air. Central heating and closed windows may exacerbate this as the air becomes even drier due to evaporation.

The Reason for the Increase in Infection rate

Why should the infection rate increase in winter? A significant factor is that people tend stay indoors more in winter often in close proximity to others. Many studies were carried out including at Yale University and the University of Sydney. Professor Michael Ward an epidemiologist at the University of Sydney explains that the droplets we exhale become smaller due to less moisture. This results in exhaled infectious aerosols staying suspended in the air for longer. In humid conditions the droplets are heavier and fall out of the air quicker.

How does Humidity Affect the Transmission Rate of COVID-19

Low relative humidity causes the mucous airways to become dryer. This impairs their function of defending the body from invading viruses.

Viruses die faster in higher relative humidity with less viral material suspended in the air

Person to person transmission increases in low relative humidity. Aerosols resulting from coughing, sneezing or even talking travel further and remain suspended longer in the air. Viruses live longer on surfaces in drier conditions.

Humidity and the Covid-19 VirusThe Response

Based on such information higher humidity levels during winter months are desirable. The use of humidifiers can be useful in maintaining a relative humidity within the recommended levels of 40 to 60%. A suitable humidifier can be found available at various outlets including at

The Conclusion

40% to 60% relative humidity appears to be ideal. However where humidity levels are higher than 60% mould may grow in indoor environments. Excessive mould growth can lead to asthma and other respiratory conditions. Always follow instructions.

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