3

According to this report

"Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens"

Similarly, a NY Times article published in 1988 states that:

"Anyone who is allergic to molds should not use cool-mist vaporizers or ultrasonic humidifiers, since both spray water into the air, Dr. Burge said. Cool-mist vaporizers pose a greater hazard since they can disperse live organisms into the air. Studies have linked the use of cool-mist vaporizers in hospital rooms with severe respiratory infections."

I understand this to mean that humidifiers increase risk of infection because they spur mold, allergens and other "live organisms" into the air - thereby increasing the amount of allergens and "toxic" substances we inhale.

1) Is there any well researched evidence to back up the claim that humidifiers spur "mold", "allergens" and "live organisms" into the air and increase respiratory infections?

2) The NY Times article states that studies have linked humidifiers to serious infections "in hospitals". Does this apply to healthy individuals as well?

3) Finally, are all humidifiers created equal in this regard?

P.S

For those of you who are unaware there are several types of humidifiers:

Steam vaporizers - uses electricity to generate steam

Ultrasonic humidifiers - oscillates 1.7 million times a second to break water into a fine mist

Evaporators - produces humidity by blowing air past evaporating water

S.O.S
  • 511
  • 3
  • 14
  • 1
    I think this needs to be rephrased a bit, to focus down on a single claim. We don't need the peripheral information about your intent to purchase, and the title should directly reflect the claim that you want to question, rather than a general request for information. If a general request for pertinent information is truly what you want, though, you might be better served to ask on the health stack exchange, rather than here at skeptics. – Ben Barden Nov 20 '18 at 21:32
  • 1
    It's unclear how a "cool mist" humidifier would "disseminate aerosols" worse than your standard evaporative one. If the water's contaminated then the water's contaminated. – Daniel R Hicks Nov 21 '18 at 01:31
  • 1
    This question is still a bit confusing. The first link you provide contains well-researched evidence to back up the claim that *relative humidity* affects the load of toxic aerosols in the air. Even if the humidifier doesn't directly spray mold in the air, it promotes the growth of mold. – Oddthinking Nov 21 '18 at 02:15
  • Can you please reference the list of types of humidifier? I am having trouble seeing how they line up with the claim. – Oddthinking Nov 21 '18 at 02:17
  • 1
    The main point here is, if the water is contaminated -- from the beginning or because the humidifier wasn't cleaned properly and in turn contaminated the water -- then turning that contaminated water into aerosol form of course disseminates the contamination. – DevSolar Nov 21 '18 at 09:48
  • 1
    @DevSolar - And note that different schemes require different degrees of cleaning/decontamination. The standard sits-on-the-floor stand-alone humidifier will develop scum (though mostly lime) in the tank over time, especially if the tank is not emptied and flushed from time to time. A spray-nozzle unit connected to "city" water and spraying into the furnace hot air duct will not put out "hazardous aerosols" (unless you're in Flint Michigan). – Daniel R Hicks Nov 21 '18 at 13:07
  • @ Daniel R Hicks evaporative humidifiers only heat and evaporate actual water and they do not propel the water with the same force as ultrasonic humidifiers @Oddthinking Humidifiers only promote growth at 60% + humidity so in most cases this should not be cause for concern. Also, even if it promotes mold growth on the ground or on certain objects it does not necessarily increase the amount of mold in the air - which is more responsible for how much mold we inhale. Of course, if you have sources that show otherwise please cite them.. – S.O.S Nov 21 '18 at 16:21
  • Hmmm... I assumed humidifers typically pushed relative humidity up above 60%, but I am now unwinding that assumption. I also assume mold growth on surfaces leads to more mold spores, leads to more mold in the air. I haven't any specific references to support that. – Oddthinking Nov 21 '18 at 16:26
  • 2
    @Oddthinking There are many low cost humidifiers available today that have inbuilt sensors that detect amount of humidity in the air and adjust output accordingly. So it is relatively simple to keep a uniform and static level of humidity. – S.O.S Nov 21 '18 at 16:33
  • @S.O.S -- The typical floor model evaporative humidifier has a porous belt that is dipped in water and then a fan blows through it. I have personally put my hand in front of the output of one of these and felt a fine mist. (I do agree, though, that most humidifiers have some sort of humidistat, and it's typically set to limit humidity to 40-50%.) – Daniel R Hicks Nov 21 '18 at 20:11
  • Welcome to the site. –  Nov 22 '18 at 16:42

1 Answers1

3

In 2008, three newborns died as part of an outbreak of Legionnaires' disease in a hospital.

The source was found to be a cold mist ultrasonic humidifier.

A case study described the investigation that lead to this conclusion:

It was determined that the neonates were infected while in the nursery at the private hospital by aerosol produced by a recently installed cold-mist humidifier that was filled with contaminated water.

[...]

Use of humidifiers in nursery units must be avoided as the risk of disseminating Legionella in neonates is very high.

Of course, we aren't all as succeptable as newborn babies, but there is still a risk. A 2017 case study, Community-Acquired Cavitary Pseudomonas Pneumonia Linked to Use of a Home Humidifier explains how a previously healthy 30 year old male succumbed to pneumonia he caught from a home humidifier unit:

We asked the patient’s family to bring his ultrasonic cool-mist humidifier from home. It was noted to have a thin gray-green film coating the plastic covering as well as standing water in the basin [...] The patient was unsure when the unit had last been cleaned.

I think cases like this explain the recommendations in the quotes given.

Outside of hospitals, there are studies like this one from 1995, Home Humidifiers as a Potential Source of Exposure to Microbial Pathogens, Endotoxins, and Allergens.

While it didn't track the absolute incidence of diseases, it did examine the water found in home units:

Clinically insignificant as well as overt or potentially pathogenic microorganisms were found to colonize the reservoirs of all types of humidifiers [...] Overt pathogens isolated from humidifiers in homes included Legionella and a pathogenic Acanthamoeba.

They also examined whether these microorganisms were put in the air:

only cool mist and ultrasonic units readily aerosolized bacteria and endotoxin. Only cool mist units emitted hydrophobic fungal spores

This doesn't prove that home humidifiers are often contaminated, that the microorganisms in the air will likely infect you or that there aren't also health benefits to humidifiers that outweigh the risks.

However, I think it supports the actual claims made:

  • cool mist humidifiers can disseminate contaminated aerosols
  • cool-mist humidifiers can disperse live organisms into the air.
  • case studies have linked the use of cool-mist vaporizers in hospital rooms with severe respiratory infections.
Community
  • 1
Oddthinking
  • 140,378
  • 46
  • 548
  • 638
  • 2
    That covers the "Cool-mist vaporizers pose a greater hazard since they can disperse live organisms into the air. Studies have linked the use of cool-mist vaporizers in hospital rooms with severe respiratory infections." but it doesn't talk about the allergens or the deal with mold. – Ben Barden Nov 21 '18 at 15:16
  • Hmmm, I always thought legionnaire's was an STD. Learn something new every day. –  Nov 22 '18 at 16:32
  • 1
    Although I presume the neonates were born healthy (since the report does not state otherwise), the study only covers a tiny spectrum of overall population since there's reason to believe newborns are more sensitive to this kind of thing. It does not tell us anything about babies (3+ months) or toddlers. Also, the study says that the humidifier was filled with "contaminated" water without going into specific details. Is tap water normally contaminated? If not then this study is the exception, not the rule. – S.O.S Nov 22 '18 at 16:35
  • Isn't case study basically a kind phrase for anecdote? This isn't particularly strong evidence that humidifiers increase respiratory infection risk. –  Nov 22 '18 at 16:38
  • Also, as had been hinted on above, it doesn't tell us anything about general risk. Most of us aren't newborns in a hospital ward. –  Nov 22 '18 at 16:44
  • @fredsbend I agree. It is also very short on pertinent details. It also doesn't tell you anything about the probability of something like this happening. Is it 1 in 1,000? 1 in a million? If most hospitals use cool mist humidifiers (which are certainly the most popular in non professional settings) and this happened only once then the risk is very low.. EDIT: I basically posted this comment at the same time as @ fredsbend.. both saying the same idea.. – S.O.S Nov 22 '18 at 16:45
  • I agree with several of the comments above. Most of us are not as fragile as newborns. This doesn't tell us relative risk. My argument was weaker than that - that this study, and studies like it, are likely why the warnings are being issued. – Oddthinking Nov 23 '18 at 06:41
  • I've added another study that shows home units are found to be contaminated, to deal with the "Isn't tap water clean?" argument. – Oddthinking Nov 23 '18 at 06:43
  • 1
    I considered adding [Assessing Inhalation Exposures Associated with Contamination Events in Water Distribution Systems](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168051#pone.0168051.ref011) which tried to model the dosages that humidifers might cause, but I didn't understand it well enough to be comfortable. – Oddthinking Nov 23 '18 at 06:47
  • I've added another study to show it isn't just newborn babies. I added a longer summary to clarify where this is and isn't an answer. – Oddthinking Nov 23 '18 at 06:57
  • Great updates. I would only change the last bullet from "studies have linked" to "*case* studies have linked". Maybe I'm being to picky, but I've already upvoted. @S.O.S –  Nov 24 '18 at 15:42
  • @fredsbend: Done, although this makes it further from the original claim. – Oddthinking Nov 24 '18 at 15:51