There are tens of thousands of mold spores in the air at all times, but that's just one reason why mold is so difficult to control

• Not all mold is bad. Molds produce the antibiotic penicillin, the immunosuppressive drug cyclosporine, and much of the world's supply of citric acid. And that's to say nothing of cheese.
• But some molds, like black mold, release harmful mycotoxins or trigger allergies or asthma. The problem is that all molds - good or bad - are really difficult to control.
• For one, molds produce tens of thousands of spores, which are invisible to the naked eye. They're around you all the time. In some cities, mold counts have been as high as 125,000 spores per cubic meter.
• Plus, molds have incredibly broad diets. They love your bread and cheese, but they'll also eat paper in your walls - and even soap.
• Visit Business Insider's homepage for more stories.

Following is a transcript of the video.

Benji Jones: You could say there are two types of mold: the good and the bad.

Penicillium notatum, for example, gave rise to the drug penicillin. Which, by some estimates, has saved at least 200 million human lives.

While other molds, like Aspergillus flavus, produce toxins that can harm and even kill you.

But whether or not you want it around, mold is everywhere.

In fact, you're likely breathing it in right now. And there's pretty much nothing you can do to get rid of it.

Mold is a fungus, like mushrooms. And it's made up of thousands of threadlike filaments called hyphae. It uses those filaments like roots: to feed.

Hyphae extend into your stale bread or rotten tomato and start releasing digestive enzymes, which are actually similar to the enzymes in our stomachs.

Kathie Hodge: Molds digest their food just like we do, except if you were a mold, it would be more like just laying your face in your food and soaking up the food through your skin.

Benji: That's Kathie Hodge, a mycologist and mold maven at Cornell University.

She says that by the time you actually see that fuzzy mold, hyphae are already hard at work, deep below the surface. So cutting out the moldy part does little to harm the entire organism. Just like ripping off leaves doesn't kill a plant.

What's worse is that molds have an incredibly broad diet. Yes, they love bread. But some species also love dead skin, soap, and even the paper covering drywall.

That's according to Nicholas Money, who has authored several books on fungus.

Nicholas Money: There's a good food source for these molds lying beneath the paint, so when that structure gets wet, bam, they'll go for it.

Benji: But if there's one thing that makes mold so difficult to manage, it's this: spores. Spores are like seeds, which molds use to reproduce.

Money: They'll produce these aerial structures, like little stalks, all microscopic. And then they'll form spores at the tips of those stalks. And then, in response to airflow, those spores will be carried that they'll get up into the atmosphere.

Benji: A single mold can make hundreds of thousands of spores. So it's no surprise that mold counts in cities like Chicago can be as high as 125,000 spores per cubic meter.

Money: You've got millions of tons of these spores in the atmosphere, and it doesn't look like it, right. But yeah, if you could visualize that, it would be mind-blowing, absolutely.

Benji: And they're not just outside. They're in your home. They're everywhere. To show you what I mean, I set up a little experiment in my apartment, À la high-school biology.

These are Petri dishes, and they're filled with what's called agar, which is essentially a growth medium for mold. So, I'm very excited to place them around my apartment and see what kinds of mold will grow in them.

I put one by my bed, another by the window, and one in my bathroom. And I left them open for about an hour to collect spores.

A week later, they looked like this.

Yeah, I'm not sure if it's beautiful or absolutely disgusting.

The dish by the window had the most diverse assemblage, about 10 species, most of which are common indoor molds, according to professor Hodge. And the one by my bed - you know, where I sleep - wasn't exactly empty.

Now, this seems terrifying. But is it?

So, at least one of the molds I collected is likely Cladosporium, and according to Money:

Money: A vast proportion of the human species is actually reactive to Cladosporium. In other words, if we get enough of the spores of Cladosporium in our lungs, they'll create some kind of an allergic reaction.

Benji: And high mold counts can also trigger asthma, he says. But it actually gets worse. You see, some molds produce nasty chemicals called mycotoxins. Such as Stachybotrys, or black mold.

Hodge: Stachybotrys make airborne toxins, and they seem to also affect our health. Even our cognitive abilities are sometimes affected by high doses of mold toxins.

Benji: And it's actually these mycotoxins that make moldy food potentially dangerous.

Hodge: Some cheese molds are actually toxin producers. For example, a particular one makes a toxin called penitrem. That is a neurotoxin. So, just eating lots of moldy things without knowing what mold is growing on them is probably not a great idea.

Benji: But here's the thing. For mold to actually cause you harm, there needs to be a lot of it, even if it's toxin-producing. So most homes, like mine, are safe.

And there are a lot of molds that we don't wanna live without. I'm not just talking about penicillin. But molds like Tolypocladium inflatum, which is used to make an immunosuppressive drug called cyclosporine. And there's this one.

Hodge: This is Aspergillus niger. It's some people's favorite mold, because this mold, can you see it?

Benji: Yeah, perfect.

Hodge: It's adorable, isn't it? This mold makes almost all the citric acid that's produced in the world.

Benji: And citric acid is a really common food preservative and flavor additive. So the next time you're drinking soda or fighting off an infection, think of molds. They may be impossible to get rid of and, frankly, just straight-up gross, but we definitely don't want all of them to die.

I'm just assuming that things are gonna be grosser in the bathroom, near the toilet. So, cool.

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