Is a humidifier a source of health benefits or a danger due to harmful microparticles?

What’s the issue: the downsides of low humidity

A fundamental biological fact about humanity: Homo emerged around two million years ago in Africa during such a warm era that mixed forests thrived in northern Greenland, where mastodons roamed, and reef-forming corals flourished in the coastal seas. A warmer world, due to basic school physics, is also more humid. Thus, our ancestors were well-adapted to heat and humidity but poorly suited to cold and dryness.

Since then, humans, aside from brain development, have not changed significantly. Today, those of us living in dry climates are more likely to develop cataracts over time than those in humid climates. Recent studies by Chinese scientists have shown that a 1% increase in average relative humidity over a year leads to a 1.4% decrease in cataract incidence among people.

Clearly, the negative effects of low humidity begin here. The fewer water vapors in the air, the longer viruses can survive. American researchers found that the autumn spike in flu cases generally occurs about 17 days after a drop in absolute humidity (which also causes a drop in temperature). Naturally, the same applies to coronaviruses. And yes, flu is no trivial matter: scientific studies have shown that those who frequently contract it are at a higher risk of developing Alzheimer's disease later on.

Additionally, in dry air, tiny particles can remain airborne longer without falling, entering the bloodstream through the lungs and causing heart attacks and strokes. The list of negative effects of low humidity goes on: redness, itching, and dry skin, snoring, coughing, sweating, and so forth. However, our space is limited, so let's get to the point: everyone understands that we need to combat these unpleasant issues.

This understanding is particularly strong in Russia, as we live in one of the two coldest countries. Consequently, the humidity here is frankly poor — both in absolute terms (absolute humidity = grams per cubic meter of air) and relative terms.

How does this happen? We inevitably ventilate our homes, allowing cold air from outside to enter and warm up. Even if the outside air has 100% humidity but a temperature of minus one degree, inside, at plus 22 degrees, the relative humidity drops to 23-24%. Our species, originating from warmer, more humid Africa, feels best at 40-60% humidity.

Relative humidity levels of just 30%, which we experience in the summer from car air conditioning, can lead to minor issues like chapped lips and dry eyes. Additionally, the likelihood of contracting a viral infection or inhaling tiny particles increases significantly. Levels below 25% pose serious risks. There are no other similarly populated cold countries like ours. Therefore, it’s not surprising that 44% of the population in Russia experiences cataracts, we frequently suffer from colds in winter, and we face all the aforementioned "bonuses."

In fact, the list of problems caused by low humidity is extensive. For instance, it leads to what dentists (those who are aware of it) call dry mouth syndrome. The system that maintains dental health in the body requires regular access to saliva. But if your mouth is often dry (which is essentially unavoidable with dry winter air), there won't be enough contact time with saliva. This leads to complications: saliva doesn’t wash away food particles from the teeth, plaque builds up, and so on. Young people may still somewhat compensate for dry mouth, but this resilience diminishes with age.

Naturally, the desire to find a solution arises. "Where did you get that vaporizer in the car?" you ask a friend. "My wife gave it to me: she cares about my health," he replies. This concern extends even further into homes. It makes sense: if there’s a decent frost outside with humidity at 20%, akin to the Sahara Desert on a satellite map. People even feel psychologically uncomfortable washing themselves in such dryness, as we know from scientific research.
Unfortunately, this is one of those cases where good intentions lead our foreheads to the nearest wall.

Ultrasonic Sahara

The fact is, the simplest and most technological method for evaporating water indoors or in a vehicle today remains ultrasonic. However, this method has a significant drawback: like "cold fog generators," it does not actually vaporize water into water vapor but merely mechanically sprays tiny droplets of liquid water into the air.

From a humidification perspective, this doesn’t change much: the mucous membranes of your nose still receive water. But from the standpoint of air composition, the difference is substantial. Water always contains dissolved substances. An ultrasonic humidifier (which is not really a humidifier but an atomizer) injects water into the air along with the dissolved substances in it. The water droplets gradually evaporate, and the dissolved substances transform into tiny particles.

These very tiny particles, which we mentioned earlier, can enter the bloodstream through the lungs. Of course, some consist of substances that are somewhat soluble in blood, such as calcium, which is often found in tap water. Thrombus formation is less common on such particles. However, not all impurities in water are easily soluble within us. Moreover, when they come into contact with the mucous membranes of the respiratory tract, they cause inevitable irritation.

We shouldn't forget about recent studies that show aerosol particles from ultrasonic humidifiers contain heavy metals. In this case, "heavy metals" is a broad term — aside from lead (which, by the way, can impair cognitive abilities and increase aggression), there’s also more toxic arsenic. Of course, such substances in the emissions of a humidifier are only present if they are in the water. In Russia, there are practically no lead pipes (unlike the USA), so it’s not easy to find significant amounts of lead in our water. However, other heavy elements can still be present.

As a result, if you turn on an ultrasonic humidifier at full power, after a short period, you might develop a slight cough. But that’s perhaps the least of the problems: far worse is that some of those same substances will reach the lungs and even further. It’s difficult to determine what effect this might have without a series of unethical human experiments.

However, a number of Western clinics, not waiting for such experiments, have already restricted the use of ultrasonic humidifiers. Nevertheless, we repeat: "cold fog" humidifiers are no better than ultrasonic ones, as they operate on the same principle of spraying tiny water droplets into the air instead of evaporating it.

Such measures have been taken in recent years when the availability of ultrasonic humidifiers coincided with the emergence of inexpensive portable detectors for micro-particles. It was then discovered that in a room with a working ultrasonic humidifier, the concentration of micro-particles in the air easily reaches 300-400 micrograms per cubic meter.

For comparison: the WHO considers a level of five micrograms per cubic meter of micro-particles acceptable. Moreover, five years ago, a group of scientists published a study in the journal Science Advances: it turned out that WHO standards are not actually safe. Even those who breathe air with five micrograms of PM2.5 per cubic meter are at risk of dying — about 1.5 million each year. Together with those who die from higher doses, the total reaches 5.7 million people.

And concentrations of 300-400 micrograms can only consistently be found near a smoke-emitting chimney or in the Sahara Desert. Even then, not always, only during a sandstorm. Satellite maps (as shown in the picture) indicate such situations as "very unhealthy." And that's a fact.

Thus, in the fight against low humidity, a significant problem for Russia in the cold season, we have established that ultrasonic aids in this battle may lead us to a Sahara-like environment in terms of micro-particle pollution. Naturally, a question arises: is there a way to mitigate the harm from such aids?

Safe humidifiers exist, but thousands died from them in South Korea

Theoretically — yes. Somewhere in the 1st millennium BC, the Persians began using special underground aqueducts, where air ducts led from "wind-catching towers" on the surface. As the air passed over the water, it evaporated some of it while cooling down. Then, through the outgoing air ducts, it reached above-ground buildings — typically the residences of the aristocracy.

The principle of "wind evaporation" is not only very ancient but also quite safe: only water vapor enters the air, leaving all impurities below in the liquid water. Today, evaporative air humidifiers contain a compact fan (structurally similar to a large PC cooler) and a large fabric filter connected to a water reservoir. According to the principle of communicating vessels, water reaches the fabric, which becomes wet, and the incoming air evaporates water from it. The energy consumption of such systems is extremely low, and they typically evaporate between 200 and 500 grams of water per hour.

This is insufficient for humidifying the dry winter air in