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Black Mold: Peril or Prosaic?

Donate Black mold is commonly believed to harbor many deadly diseases; but in fact removing it is often worse than leaving it.  

by Brian Dunning

Filed under Environment, Health

Skeptoid Podcast #494
November 24, 2015
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Black Mold: Peril or Prosaic?

Turn the TV to the home improvement channel, and you're liable to see work crews tearing apart old kitchens in respirators and hazmat gear, doing tens of thousands of dollars worth of demolition and sampling and testing and eradication and reconstruction. You'll hear stories of victims who inhaled or ingested black mold and developed debilitating diseases, cancers, Parkinson's, lungs filled with blood, neurologic disorders, birth defects, vision and hearing loss and organ failure, horror stories right out of the tabloids. Could this innocent looking black mold living in so many of our homes truly be the terror that some make it out to be, or is it possible that the scare is overblown?

The history of the black mold scare follows a pattern that is familiar to many who follow skepticism in pop culture. Before the mid 1990s, nobody ever heard of black mold, nobody ever got sick from it (at least not that was widely reported), and people lived their lives in homes full of mold without any ill effects, by all accounts. However, since then, it's been common for people to report being sickened by black mold. People readily spend tens of thousands of dollars to have mold removed from their homes, and all kinds of companies advertise warnings and offer eradication services as if it's a critical problem demanding immediate mitigation. We can think of three likely scenarios that might explain why we have such a big problem now that we didn't seem to have only a few years ago:

  1. The problem is as serious as reported and began suddenly in the 1990s, which doesn't seem very likely, since mold is natural and has always been a part of our environment and has always grown in our buildings;

  2. People have always been seriously sickened by mold exposure, but prior to the 1990s it was misdiagnosed and unreported; or

  3. Mold is the same size problem at some modest level that it has always been, but an undue amount of reporting and sensationalism has surrounded it since it was cast into the public spotlight in the mid 1990s.

One of these is probably true.

Looking back at the history of mold reporting, we can indeed see that there was an explosion of publication beginning around 1994. Scientists from the CDC published an article called "Acute pulmonary hemorrhage/hemosiderosis among infants" in the journal Morbidity and Mortality Weekly Report, in which they described a cluster of ten infants in the Cleveland area who contracted this bleeding lung disease in 1993, and attributed it to spores from the mold Stachybotrys chartarum. The infants all lived in homes that had had water damage during the six months prior to diagnosis. This article was widely circulated by the mass media. It was the finger pulled from the hole in the dike, and from that moment on, black mold has been broadly believed to cause this, and many other, pulmonary and systemic illnesses. Even "sick building syndrome", a controversial diagnosis that had been around since the 1970s, was largely reworked to incorporate mold as one of its primary antagonists.

It's what happened next that makes it match the pattern of other sicknesses popular in the skeptical literature, and you might be able to guess what it was. Other researchers found that the 1994 article was flawed, deeply flawed; and probably wrong. It's now the consensus that there is no proof that mold was responsible for giving anyone lung hemorrhaging. They found the infants in the study probably did not all have the described condition; they found the water damage to the homes was anecdotal and was not associated with any measured levels of mold; control homes did not have significantly different levels of mold; and most of all, there was no evidence that these particular infants had been exposed to unusual levels of mold.

What happens in cases like this? Does the worldwide media trumpet the new finding that says the earlier sensational news was wrong? Of course not; it was probably busy reporting new sensations. The new finding was ignored by the mass media, despite being rock-solid in the scientific literature. Black mold as the incredibly dangerous cause of all sorts of fearsome diseases had become firmly rooted in the public consciousness, where it has remained ever since.

So does that mean black mold is totally harmless? Of course not; nothing is. It's a potential allergen like many others for some people, and can present a bit more of a risk for some others. So let's look closer at it and see exactly what it is, and what are the real risks to health that it might pack.

Go to any lumberyard and look at any pile of construction grade lumber. You'll see that black mold is found all over the place, yet nobody seems too concerned. Why is this? It's because there are lots of kinds of mold, around 100,000 species, about 1,000 of which are common in the United States. Molds are a type of fungus, and like all fungi, molds get their energy by breaking down an organic material they live on, and reproduce via airborne spores. They require moisture. Wood is a great place to find mold, because it's chock full of the nutrients they love, and it hangs onto moisture really well. Those molds might be black, gray, yellow, brown, or even red.

Molds themselves are not dangerous, only the spores they release into the air when they reproduce. And even then, only a few species have spores that are potentially harmful, and these are called mycotoxins. These mycotoxins are the key to mold problems. In some cases, they can trigger minor upper respiratory tract symptoms — basically coughing and wheezing — in otherwise healthy people.

Most people don't have any reaction to even the worst molds, and can coexist happily: Remember, we all breathe some mold spores everywhere we go every day; reactions are pretty rare for most of us. The Centers for Disease Control and Prevention describes the possible health effects of mold:

People who are sensitive to mold may experience stuffy nose, irritated eyes, wheezing, or skin irritation. People allergic to mold may have difficulty in breathing and shortness of breath. People with weakened immune systems and with chronic lung diseases, such as obstructive lung disease, may develop mold infections in their lungs.

That's the extent of it. Notice what's missing from that list. Serious medical conditions like bleeding lungs, or other conditions like chronic fatigue, insomnia, memory loss, Parkinson's disease, birth defects, and various cancers, have not been linked to mold, no matter how many websites and Facebook memes tell you they have. With that said, asthma and allergies can be serious to people with particular susceptibilities. Those people are those who already have asthma or allergies or other chronic breathing conditions. There is another group of people who need to be wary of mold, and that's a group whose immune systems are sufficiently compromised that they're at risk of a lung infection. These are people taking immunosuppressant drugs such as organ transplant recipients, people who have HIV, and cancer patients taking chemotherapy.

So if you find that you do have mold, and you've determined that it is causing a problem for someone in your household, what should you do? Opinions differ based on who you ask. Unsurprisingly the recommendations for the most radical and costly interventions tend to come from companies selling these services. The best answer comes from science. You're never going to get rid of the mold, so there's little point in trying. If a particular mold species is in your home, it's there because spores in your area brought it there, and they will do so again; even if you burn your house down and build a new one, those same spores are going to come right back. Instead, you need to make your home a less inviting habitat for mold. The way to do this is to eliminate the source of the moisture. If you have a leaking pipe, fix it. If there's water in your walls, call a plumber. If you live in a wet climate, install a moisture barrier. Once the moisture is out of the environment, the mold will stop growing and producing spores. You truly don't even need to remove the mold; you need to fix the source of the water.

Testing of the mold is not recommended. The reason to test it would be to see if it's one of the dangerous species, but testing is expensive, and the type of mold is not a useful predictor of risk. It's your susceptibility and the conditions that count. If someone is having an adverse reaction, the mold should be removed and the moisture problem fixed; if nobody is having a reaction, there is no reason to spend money on testing or eradication.

If you do want to remove mold, it's surprisingly easy. Simply spray it or scrub it with a diluted bleach solution, and that will do it. It is recommended that you wear rubber gloves and goggles, but that's more to protect you from the bleach than from the mold. You should also wear a dust mask to protect you from particulates (mold and otherwise) that you'll kick up by cleaning. You don't need to hire a contractor unless the job is bigger than your spray bottle or you want to take down walls. But mind you, the mold is natural, and it's there because that species has spores in your area, so it will grow right back unless you stop the source of the moisture that it requires.

Some websites recommend special organic diets to treat mold allergies. Such advice has no scientific or medical basis at all, and should be ignored.

I think of black mold the same way I think of rats or mice. If someone in the house gets bitten or develops an allergy to them or they cause some other problem, then you need to get rid of them or find some way to address the situation; but you don't tear your kitchen apart because there are mice in your neighborhood that aren't causing anyone a problem. There are always going to be rats and mice in every neighborhood, even after you call the exterminator; and there is always going to be mold in every room of every house, even after than expensive eradication and rebuild. There's no such thing as a house without mold, so don't try to create one. And also, don't pay attention to sensationalist headlines like "Peril or Prosaic?" because those are usually false dichotomies, and the truth is more nuanced.

By Brian Dunning

Please contact us with any corrections or feedback.


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Cite this article:
Dunning, B. "Black Mold: Peril or Prosaic?" Skeptoid Podcast. Skeptoid Media, 24 Nov 2015. Web. 19 Jun 2024. <>


References & Further Reading

CDC. "Facts about Stachybotrys chartarum and Other Molds." Mold. Centers for Disease Control and Prevention, 18 Oct. 2005. Web. 4 Nov. 2015. <>

CDC. "Acute pulmonary hemorrhage/hemosiderosis among infants -- Cleveland, January 1993-November 1994." Morbidity and Mortality Weekly Report. 9 Dec. 1994, Volume 43, Number 48: 881-883.

CDC. "Update: Pulmonary Hemorrhage/Hemosiderosis Among Infants --- Cleveland, Ohio, 1993--1996." Morbidity and Mortality Weekly Report. 10 Mar. 2000, Volume 49, Number 9: 180-184.

Heseltine, E., Rosen, J. WHO guidelines for indoor air quality: dampness and mould. Copenhagen: World Health Organization, 2009.

Robbins, C., Morrell, J. Mold, Housing & Wood. Portland: Western Wood Products Association, 2006.

Rosenblum Lichtenstein, J., Hsu, Y., Gavin, I., Donaghey, T., Molina, R., Thompson, K., Chi, C., Gillis, B., Brain, J. "Environmental mold and mycotoxin exposures elicit specific cytokine and chemokine responses." PLoS One. 26 May 2015, Volume 10, Number 5: e0126926.

Shi, C., Provost, N., Desroches, T., Miller, J. "Quantification of C. globosum spores in house dust samples." Annals of Agricultural and Environmental Medicine. 1 Jan. 2014, Volume 21, Number 3: 525-530.


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