Window air conditioners: a health hazard

The Mayo Clinic said “home and car air conditioning units don't use water for cooling,” suggesting they don't pose a risk for Legionnaires' disease. This is partially false because modern window air conditioners commonly collect condensed water so it pools in the drain pan (bottom part of the frame) until the level rises high enough to be struck by fan blades that intentionally sling water against coils to increase the unit's efficiency.

The problem is that the drain pan remains wet during much of the cooling season. Being substantially horizontal (inclined just enough to prevent water from draining inside), the drain pan collects airborne dust and all of the hazards in it, including mold spores, bacteria, and stuff kicked up by lawnmowers and leaf blowers, which includes decaying plant and animal waste as well as their urine and feces.

Wet + horizontal = highly effective trap for crap.

The moisture is conducive for mold and germ proliferation. As they grow, they don't stay there because window air conditioners typically permit users to bring in outside air that enters just above the pool of filthy water. But remember the water slung by fan blades? Some of it is aerosolized into a mist that mixes in with the incoming air. And where does it go? Into your home, sinuses, lungs, and elsewhere.

I learned this lesson the hard way. One of my biggest mistakes in life was assuming that things sold in stores are safe. Window air conditioners are not. I didn't notice any problems the first two years of use, but whenever I used it this year, for days afterward I would frequently cough and had a persistent feeling that I was on the verge of one. If I didn't use the AC for several days, the cough would resolve. After several cycles of this, I knew the air conditioner was the source of the problem. Inspecting it, I was horrified by what appeared to be black mold extensively contaminating the drain pan as well as the bottom of the evaporator coil inside my home along with the expanded polystyrene duct (most folks would call it Styrofoam) directing cold air inside.

My first thought was: just clean it. Then reality sunk in as I realized that I could spend a week cleaning it and not remove all germs from the bewildering number of nooks and crannies, many very inaccessible. I watched videos of handymen cleaning window air conditioners, satisfying themselves with incomplete removal, as if exposing home occupants to a lower level of pathogen contamination is acceptable. The consensus is that thorough cleaning is virtually impossible.

Cough, wheezing, shortness of breath, and sneezing are not the worst worries because Legionella can cause infections, such as Pontiac fever and potentially deadly Legionnaires' disease. You may dodge that bullet but you almost certainly won't escape the risk of mold that is so ubiquitous it reliably proliferates whenever given what it needs to survive: moisture, a bit of warmth, and something organic to feed on — supplied by stuff wafting in air.

Incidentally, it isn't just outside air that is contaminated; interior air is, too. As it enters and contacts the evaporator coil, room air loses some of its moisture (that's how it dehumidifies), condensing onto the coils and dripping down along with the dust and germs in your air that sticks like a magnet to the moistened metal.

Cough can disrupt sleep, potentially impairing school or work performance, and the resulting tiredness can contribute to car accidents or other problems, such as irritability affecting relationships.

Some people are fond of using mold control products. I am not one of them because they can't thoroughly clean air conditioners, and they often contain isothiazolinones that are strong sensitizers capable of inducing allergies. Researchers have also linked them to endocrine disruption and neurotoxicity (see references at the end). Cool air but potentially less IQ? I'll pass!

Reputable manufacturers would therefore not make such hazardous window air conditioners but instead redesign them to make thorough cleaning quick and easy without disassembly. Because they don't, countless people see their doctors for coughs or other problems treated with medicines that are often costly and produce side effects. Unfortunately, very few doctors understand the extent to which the exposome influences health. This is but one of thousands of exposome factors overlooked by doctors as well as unscrupulous manufacturers producing needless problems.

Corporate buyers could play an essential role in ending this problem by refusing to sell products that endanger customer health. Using their corporate clout, they could compel manufacturers to invent safe ways to cool air.

It can be done. Disgusted by what I saw in my air conditioner and others online in considerably worse condition, it took me less than one hour to come up with solutions. One was a simple way to modify existing window air conditioners to markedly reduce indoor air contamination. Others were various design changes to make cleaning very easy, even without disassembly. Yet another was a way to cool without any potential of mold or bacteria contaminating inside air.

So why don't air conditioner manufacturers do this? Because if they make plenty of money selling junk, why invest in making better products? There is no commercial demand for them because very few people make the connection between window air conditioners and their health problems, and rarely do their doctors put two and two together.
I would bet that less than 1% of consumers frequently disassemble and thoroughly clean their window AC units, which means that over 99% of them will eventually be exposed to needless hazards.

Doctors Carlos Ruz-Pau and Jorge Parellada reported a patient who “became infected [with Legionnaires' disease] via her window air conditioner” resulting from “aerosolized water particles.” Legionellosis is often missed; I read estimates that over 90% of cases are not properly diagnosed.

Compounding the difficulty of that, such infections may present with non-respiratory symptoms and signs. One example: Gastrointestinal Legionella: An Underecognized Entity and Cause of Secretory Diarrhea: A Case and Review of the Literature. If you have nausea, vomiting, and diarrhea triggered by a window air conditioner, few doctors will make the connection. Or “confusion or other mental changes,” chest pain, shortness of breath, headaches, muscle aches, fever, tiredness, and just plain not feeling well. If you consider the diverse spectrum of problems resulting from airborne bacteria and mold, it isn't surprising that window air conditioners cause so many difficulties in so many people.

Of many things that harm the body and brain, do you ever wonder exactly how the damage is done? One of the most common is inflammation. The immune system kills germs via inflammation (1, 2, 3). Notably, this doesn't occur only with infections producing symptoms letting you know that you are sick; it also occurs with subclinical infections with no symptoms.

People who aren't immunocompromised usually do a good job of clearing pathogens, but when germ exposures go on and on, persistent acute inflammation can lead to chronic inflammation (1, 2, 3, 4). Chronic inflammation accelerates aging (1, 2, 3, 4).

Consequently, chronic exposures to mold and bacteria are not good. This dovetails with common sense and helps explain the upsurge in general human health traceable to improve sanitation, especially from the mid-1800s to the early 20th century. Most folks in developed nations now live in reasonably clean conditions but those with window air conditioners can have horrible air quality triggering chronic inflammation that accelerates aging inside and out.

This is yet another manifestation illustrating how manufacturers would better serve customers by consulting doctors who know how countless aspects of the real world adversely affect health.

Beware of single-hose portable air conditioners

Portable air conditioners are a popular alternative to window AC units. One of the great mysteries is why the United States government so eager to regulate appliance efficiency (to the point that it hobbles dishwasher efficacy) does't prohibit single-hose portable air conditioners that are notorious energy hogs. My guess is that legislators don't understand why they are so wasteful. They make sense in very few circumstances. One of them: you rent a small room or two from a homeowner you can't stand. Your rooms will get colder but the warm air exhausted outside creates a vacuum that pulls in air from other rooms, creating a vacuum in them that pulls in warm and often humid air from the outside, often making those other rooms even worse than they otherwise would be. If you care about whole-house comfort, single-hose air conditioners are definitely a bad idea.

This makes me wonder: why would corporate buyers — the ones who select what their stores will sell — stock products with inherent design flaws when better alternatives are available? Dual-hose portable air conditioners are roughly the same price but substantially more energy efficient, resulting in markedly less net cost of ownership while delivering superior comfort to home occupants, obviously best in the installed room but with other rooms cooled and dehumidified to some extent (better if the HVAC system circulates air throughout the house).


  1. Isothiazolinone Biocides: Chemistry, Biological, and Toxicity Profiles
  2. In Vitro Neurotoxicity of Methylisothiazolinone, a Commonly Used Industrial and Household Biocide, Proceeds via a Zinc and Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase-Dependent Pathway
  3. Isothiazolinone dysregulates the pattern of miRNA secretion: Endocrine implications for neurogenesis
  4. Panasonic: Mould in your air conditioner is more common than you think
    Excerpt: “Panasonic air conditioners equipped with an internal cleaning function with nanoe™ X Generator Mark 3 can inhibit the growth of mould inside the air conditioner.”
    Comment: Panasonic's nanoe™ X technology generates highly reactive hydroxyl radicals. I wondered: safe? Decide for yourself:
    (a) Environmental Implications of Hydroxyl Radicals (•OH)
    Excerpt: “… considering the fact that people spend so much more time in dwellings than outside, the impact of the reactivity of indoor hydroxyl radicals on health and well-being is another emerging research topic of great concern.”
    (b) Unexpectedly high indoor hydroxyl radical concentrations associated with nitrous acid
    Excerpt: These findings force a change in our understanding of indoor air quality because the reactivity linked to OH [hydroxyl radical] would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air.
    Comment: This strikes me as more evidence that even otherwise reputable manufacturers are reckless with health.
  5. Mother Jones March 1, 2021: Are Schools' Fancy New Air-Scrubbing Devices Really Effective—and Safe? A scientist airs her concerns about the surge of products that supposedly kill airborne viruses.
    Excerpt: “What they're trying to do is add chemistry that oxidizes organic molecules … But it's hard to oxidize organic molecules all the way. … There's a lot of toxic byproducts. Take a big organic molecule like limonene—the molecule that makes anything citrus scented. It's all over personal care products, and when you cook. It's very prevalent in the indoor environment. You interact it with one of these ozone or [hydroxyl radical] generators, and you're going to make formaldehyde.”
    Comment: Formaldehyde has multiple toxic effects: one of them is damaging the brain. Corroborating that:
    (1) A Novel Mechanism of Formaldehyde Neurotoxicity: Inhibition of Hydrogen Sulfide Generation by Promoting Overproduction of Nitric Oxide
    (2) The toxic effects of formaldehyde on the nervous system

    Excerpt #1:
    “Also, the oxidants themselves are quite toxic. … hydroxyl radicals are something that you would not want reacting with the tissues of your lungs.”

    Comment #1:
    That's the first thing I thought of: hydroxyl radicals would essentially fry airborne organic matter but do nothing to my lungs? It made no sense!

    Excerpt #2:
    “Of particular concern to the authors are anatomists and medical students, who can be highly exposed to formaldehyde vapor during dissection sessions.”

    Comment #2: More evidence that medical schools are dunces about basic aspects of health. It's not just the formaldehyde exposure in anatomy labs; it is that I invented technology to safeguard people from airborne pathogens that can also protect them from many other airborne hazards, including formaldehyde. With millions of doctors in the world, why am I — operating on a shoestring budget in the middle of nowhere — seemingly the only one with a very effective solution to this old problem?

    Unfortunately, medical schools omit other crucial aspects of how formaldehyde adversely impacts health. For example, formaldehyde is common in modern building products — that's well-known. What doctors miss is other sources of formaldehyde in homes stemming from their construction.

    Doctors should be able to integrate what they learned in chemistry with how that interacts with wood and a contaminant introduced into it (in factories and at building sites) that catalyzes formaldehyde generation. Knowing all this, doctors with common sense should be able to instruct manufacturers and builders how to substantially reduce the problem — but when they don't know of the problem, they don't seek solutions.

    I strongly believe that doctors should possess doctor-level knowledge, and should be able to think for themselves by connecting the dots between the scientific literature and the real world. When they don't, people suffer. Some become patients whereas others just suffer in silence, perhaps disappointed in themselves that they didn't get into medical school or otherwise achieve the career of their dreams because of formaldehyde neurotoxicity.

    (3) Association Between Occupational Exposure to Formaldehyde and Cognitive Impairment
    (4) Formaldehyde toxicity in age-related neurological dementia
    (5) Formaldehyde and Brain Disorders: A Meta-Analysis and Bioinformatics Approach
    Excerpt: “Environmental exposure to the pollutant formaldehyde, an emerging neurotoxin widely used in industry, is suspected to play a critical role in mediating these disorders [Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis = ALS] …”
  6. An article underscoring the importance of keeping cool: Exposure to heat and cold in early life may affect development of white matter in the brain
    Related: Heat Waves Are Making Restaurant Kitchens Unsafe. Workers Are Fighting Back.
The views expressed on this page may or may not reflect my current opinions, nor do they necessarily represent my past ones. After reading a slice of what I wrote in my various websites and books, you may conclude that I am a liberal Democrat or a conservative Republican. Wrong; there is a better alternative. Just as the primary benefit from debate classes results when students present and defend opinions contrary to their own, I use a similar strategy as a creative writing tool to expand my brainpower—and yours. Mystified? Stay tuned for an explanation. PS: The wheels in your head are already turning a bit faster, aren't they?

“The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.”
F. Scott Fitzgerald

Reference: Imagining dialogue can boost critical thinking: Excerpt: “Examining an issue as a debate or dialogue between two sides helps people apply deeper, more sophisticated reasoning …”

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