Allow to start start by again reiterating that I am a proponent of the WHO guidelines of ‘Social Distancing’ and ‘Hygiene’.

Undisputed scientific research has proven that SARS-CoV-2, causing the illness COVID-19, spreads through 2 mechanisms, namely;

1. Direct contact (direct person-to-person contact such as handshaking)

2. Expiratory droplets (sneezing/coughing droplets, travelling a few feet)

But I also believe that there is an important third route; Microscopic droplets; aerosols/droplet nuclei/non-sedimenting droplets. These remain airborne in unventilated areas.

The Netherlands’ 1.5-meter social distancing aims to prevent (I) and (II) and has been successfully applied. Up until recently there was no peer reviewed research available about microscopic droplets with regards to COVID-19.

Earlier research has proven that microscopic droplets do exist in Influenza viruses. But academics, for good reason, were hesitant to compare influenza to COVID-19. Until recently. New research, done by various universities, now shows that expiratory droplets, containing a virus, include water, salts and organic material.

If, upon expiration, some of the water content evaporates, the microscopic droplet becomes small and light enough to stay suspended in the air. This is how microscopic droplets are created. Microscopic droplet concentration in the air builds up (called ‘Viral load’), increasing the risk of infection, particularly if the air is stagnant as in many indoor environments in public places with insufficient and inefficient ventilation.

The effects of Humidity on aerosols. How they fly…

For the sake of readability, I’ll use the term ‘aerosol’. An aerosol is – in essence – an expiratory droplet that lost its ‘weight’ and has become airborne. This understanding is gradually becoming accepted. In many countries people, as a result, are talking about ‘ventilation’ as a way of fighting aerosols. Herein lies a new problem. A lack of understanding about the dynamics of aerosols.

An expiratory droplet that lost its ‘weight’ has lost its ‘water-weight’. Here’s where humidity comes into the equation. In an earlier blogpost i explained how evaporation works. Now allow me to explain how humidity plays into this dynamic. Your clothes dry faster in a dry environment, right?

The same applies to aerosols. The dryer the air, the more respiratory droplets evaporate, the more aerosols, the higher the viral load in the air, the more aerosols you inhale, the higher the chance of getting infected.

The opposite is also true. The more moisture in the air; less droplets that evaporate, less aerosols, lesser viral load in the air, less aerosols you inhale, less chance of getting infected.

That is why – in big part – we have less respiratory virus infections in summer (high humidity) and higher infections in winter (low humidity). It is the reason why i was able to predict the ‘second coronavirus wave’ in week 44 (end of October) 2020. Sunshine (Solar Radiation) plays an important role as well. But that is another topic, for another day.

Another effect of Humidity on respiratory viruses

Humidity has another, important, overlooked effect on Respiratory Viruses; Influenza and SARS-CoV-2. These are ‘Enveloped Viruses’, which is visually comparable to a ‘balloon’. The virus is basically contained in its own little ‘balloon’. Researchers figured out a long time ago that humidity also affects these enveloped viruses, namely that a higher (but not absolute) humidity is bad for the longevity and ability to infect of the virus.

A low humidity does the following to these respiratory-enveloped-viruses;

The salts. The salts in the respiratory droplets, when the aerosol is formed, actually creates a shield that protects the virus while airborne. When the aerosol hits your mucous membrane (ie. the tissue in your lungs for example. Which I’ll just call ‘Slime’ for now), the salt-shield actually allows the virus to penetrate deeper. When it hits its destination, the slime actually hydrates the salt-shield, dissolving the shield and allowing the virus to infect your tissue very efficiently. The opposite is also true; High humidity avoids the salt-shield getting formed.

A high humidity does the following to these respiratory-enveloped-viruses;

Surface inactivation. An enveloped virus loses its infectivity dramatically (up to four orders of magnitude) due to aeration. The hypothesis is that enveloped viruses are likely to accumulate at the surface of droplets, where “unbalanced forces” acting on the virions (ie. the viral particle itself) may be strong enough to produce inactivation through irreversible unfolding and rearrangement of molecules. Basically the ‘Balloon’ bursts. And the virus can’t live outside of its balloon.


Our mucous membranes (Mucosa), is a natural barrier against viruses. Think of it as a “bunker” made of slime. The bigger and stronger the “bunker”, the better the protection. Slime, as you know, contains water. The more water, the more slime, the thicker and stronger our “bunker”. That is also why we are more susceptible to respiratory viruses in winter. Due to the low humidity, our “bunkers” are less large and strong. Increasing the humidity ensures that our “bunkers” remain strong.

So whenever people talk about ventilation, tell them;