This is the time of viruses, and here I want to raise the following question: can an air humidifier protect you from viruses. The answer might surprise you, keep reading.
There was a scientific paper published a decade ago, long before the actual coronavirus situation. For the reference, the full title was Effects of Air Temperature and Relative Humidity on Coronavirus Survival on Surfaces. This study was related to severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) and not to the actual COVID-19 which is in the same group known also as CoV-2.
They wanted to know how virus survival is affected by air temperature and relative humidity. So this is important also for a typical situation at home because both of these parameters you can control, more or less.
But there is a bit more to this, in the actual study they did not use the SARS-CoV virus. For some reasons, they used two surrogate viruses, transmissible gastroenteritis virus (TGEV) and mouse hepatitis virus (MHV).
Without getting into too many details, the main results (for the point of this text) are presented in this graph below which suggests the following:
- With humidity at 50%, the number of viable viruses was the lowest. So there is an optimal humidity range with respect to protection from (some) viruses.
- At 4°C, the infectious virus persisted for as long as 28 days.
- The lowest level of inactivation occurred at 20% relative humidity. In other words, viruses love dry air.
- Inactivation was more rapid at 20°C than at 4°C at all humidity levels.
- Both viruses were inactivated more rapidly at 40°C than at 20°C. In simple words, viruses tend to suffer at higher temperatures.
- But this is not all so simple, there is also a greater survival range at a very high humidity level of around 80% as compared to the 50% humidity level.
A bit more about harmful dry air effects
Viruses are sub-micron sized and they can attach to small pollutants and particles in the air. For example, the coronavirus is around 125 nm in diameter, and this is 0.125 microns. Just for comparison, pollen particles are typically in the range of 2 – 20 microns, but there are much bigger ones.
So from the perspective of viruses, these are huge objects, and viruses can accidentally land on them, and then they can be carried by air. This is how they can get into your body together with other pollutants when you breathe.
On the other hand, did you know that tobacco smoke particles (aerosols) from a cigarette have a distribution of sizes in the range 0.1 – 1 micron, with a peak around the size of the coronavirus. More about this is available in C.H Keith and J.C. Derrick, J. Colloid Sci., v. 15 (4), 340-356 (1960).
No doubt you have had a chance to watch how a cloud of smoke from a cigarette spreads through the air. Imagine this is a cloud of viruses, they are of the same size, so there is no reason to assume that this is not possible.
Now back to the dry air issue. In the case of dry air, particles in the air are lighter than in the case of air with more humidity. This is because there is less water vapor condensation on such objects. Note that water molecules are of the size around 0.3 nanometers, and this is 400 times smaller than the size of the virus.
There is always some natural air circulation even in a closed space like a room at home, so such dry particles can easier be carried by air, and the same holds for the viruses and other germs, and also for those pollutants that are behind allergies.
What this all has to do with air humidifiers?
If you have read the text above carefully, the answer should be obvious. But if you did not quite get the idea, here are the main conclusions:
- There are reasons why most of the air humidifiers’ manufacturers suggest keeping the humidity in the range 40-60% level. With such humidity, and at typical room temperatures, it is less likely that viruses will survive for a long period of time. So using air humidifiers at home makes a lot of sense.
- In the case of dry air, pollutants and viruses are easier carried by the air, so adding moisture in the air will make them heavier and they will have less chance to spread around.
As you see, there are at least two good reasons for keeping humidity at a higher level, not to speak about its positive effects on the skin, on respiratory organs, etc.
But you can do even more to improve the quality of the air at home and to avoid those negative effects discussed above. There are devices for home use described as air washers and air purifiers, and some of them are cleverly designed so that you have both a humidifier and a purifier in one device. They add vapor in the air, and at the same time they physically remove pollutants and particles from the air, so these are true 2-in-1 devices.
As for the humidity level in the room, no need to guess, you will need some instrument. Use some reliable hygrometer, there are many of them on the market.
All in all, as you realize, indications are strong that keeping room air humidity in the mid-range can help against some of the viruses. Will this really help in the case of the current COVID-19 thing? Well, nobody knows yet. We might read about similar studies in the coming years. As for now, use common sense and reliable facts, and act accordingly. One more thing to add, I have been through this with the virus, and can tell you it is hard.
Thank you for reading. You might want also to check my text about the differences between an air humidifier and purifier. See also my separate text about air purifiers and viruses. Please let me know if you have any question, there is a comment box below. Have a nice day.