Based on an episode of Mold Money: “Yes – All Molds Can Produce Mycotoxins — And Why That Matters.”
Most people in the “mold world” have heard some version of this:
- “Only certain molds are toxic.”
- “Don’t worry, that’s just a ‘common’ mold, not the dangerous kind.”
- “Your urine test shows this mycotoxin, so you must have that mold in your house.”
Those ideas are comforting. They make the world sound simpler: a few bad actors, a few “safe” molds, and a test that neatly connects the dots. The problem is, that’s not how mold, toxins, or science work. In this episode, Daniel Stih explains a controversial but scientifically sound point: All molds have the potential to produce mycotoxins.
Not all the time. Not in the same amount. Not under every condition. The line between “toxic mold” and “harmless mold” is largely a human invention. Misunderstanding that leads to bad testing, bad assumptions and bad decisions.
What a Mycotoxin Is
Let’s start with the word itself:
- “Myco” = fungus / mold
- “Toxin” = something that can harm another organism
In plain language, a mycotoxin is simply a toxin produced by a fungus. In the mycology literature, definitions often get more specific, for example:
- A mycotoxin is often described as a secondary metabolite (a chemical a fungus produces after basic growth.)
- That metabolite can cause harm in vertebrate animals (including humans) when they’re exposed via food, inhalation, or other “natural routes”
Notice what this does not say. It does not say only a few “special” molds can make toxins. It does not say we’ve cataloged all possible toxins. Some mycology references point out that if we broadened the definition to include more animals and more effects, we’d end up including all fungal secondary metabolites, and the word mycotoxin would lose its “special” meaning. In other words, the more honestly we look at it, the less that neat “toxic vs non-toxic mold” split holds up.
The Mushroom Example: “Safe” Foods That Still Make Toxins
Consider everyday button mushrooms, the common mushrooms you see in the grocery store: White button, baby Bella, and Portobello. These are each the same species of Agaricus bisporus at different stages of maturity. Most people think of them as safe. We put them on salads, on pizza, in sauces. Yet they can produce a compound called agaritine, which is considered a potential carcinogen in high doses in lab animals, is present in mushrooms at low levels, and is reduced by cooking (heat can lower levels dramatically).
Does this mean you should panic and never eat mushrooms again? No. It means a fungus can be simultaneously “safe” in normal doses and capable of producing a toxin. The same species can be part of your dinner one day and, under different circumstances, be a toxic concern in a study or outbreak.
There isn’t a clean dividing line between “toxic species” and “safe species.” Risk depends on dose, context, and exposure, not just the name of the fungus. If that’s true for mushrooms, it’s true for other molds too.
Secondary Metabolites: Why Toxins Are Not Always Present
The mold grows first. It eats, expands, and colonizes. Only under certain conditions does it start making extra chemicals (secondary metabolites), including mycotoxins. Those conditions might involve competition with other microbes, stress, crowding, or lack of nutrients. It might be environmental changes (temperature, moisture, etc.).
Even molds that are famous producers of mycotoxins (such as Aspergillus or Stachybotrys species, do not produce toxins constantly just because they’re present. You can’t look at a mold and automatically know what toxins are there. You cannot reliably go backwards from a mycotoxin in urine and say,“It must have come from this species in that wall of your house.”
“Toxic Mold” vs Reality: How Language Misleads
Terms such as “Toxic mold”, “Black mold” and “The bad molds”are media-driven, emotionally loaded phrases. Stachybotrys became “black mold” in headlines, despite that lots of molds can appear black and lots produce unpleasant or harmful compounds.
“Toxic mold” language makes it sound as a few molds are evil and the others are mostly harmless. In reality many molds trigger allergies and can irritate airways. All molds have potential to produce toxins under the right conditions,
When someone says, “Don’t worry, it’s just Cladosporium / Alternaria / some ‘common’ mold,” what they mean is, “This species isn’t on the short list from old food-poisoning outbreaks.” That’s different from, “This mold is incapable of producing harmful substances.” Scientifically, that second statement is false.
How the Term “Mycotoxin” Got Narrowed (and Weaponized)
Historically, the word mycotoxin gained attention during serious food-related outbreaks in which moldy grains that killed livestock, Aflatoxins were present in contaminated crops, and the poisonings were obvious and acute. Governments, scientists, and doctors needed a word that said, “These fungal toxins that are making people and animals very sick through food.”
The word mycotoxin became associated in practice with specific, documented foodborne crises, and a list of molds and toxins that had already caused dramatic problems.That list is not a list of “the only molds that can make toxins.” It’s more like: “the molds we’ve already caught in the act in dramatic situations.”
Fast forward to modern indoor air, chronic illness, and lab testing. People talk about “mycotoxins” as if the word only applies to a narrow group of species and chemicals. Lab panels test for a small set of known toxins. Results get interpreted as if absence of that one toxin = safety, or presence = proof of a specific mold in your house. These are over interpretations.
Why “All Molds Can Produce Mycotoxins” Matters in Real Life
Misunderstandings about mycotoxins lead to bad decisions and wasted money.
1. You cannot use urine mycotoxin testing to pinpoint mold in a house
Mycotoxins can come from food, not just buildings. Multiple molds can produce similar or overlapping toxins. Toxin production is conditional, not guaranteed. When someone says, “You have Ochratoxin A in your urine, so you must have this mold species growing in your wall,” that’s not science. That’s a story.
2. Focusing on “toxic species” distracts from the real question
The real practical question in mold inspection should be, “Is there actual mold growth in this building? Where is it? And how do we remove it?” Whether the mold is one of the “famous” species or a “common” one, if it’s growing indoors, it can contribute to inflammation, allergy, and irritation. It can potentially produce secondary metabolites, including toxins. If you’re sick and there’s mold growth indoors, that’s what matters, not whether the lab sticks the “toxic” label on it.
3. You can always find something if you look hard enough
If you test aggressively enough, you will find mold spores, bacteria, mycotoxins, and chemical residues. The presence of something detectable doesn’t automatically mean, “This explains all your symptoms.You must perform a particular treatment or buy a particular product.” Let’s stop letting one molecule or one word (“mycotoxin”) hijack the whole conversation.
A Better Way to Think About Mold and Health
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If you’re sick, follow your doctor’s advice.
Understand that “mycotoxin” is not a magic answer. It’s a piece of a complex puzzle. -
Don’t obsess over which mold species is “toxic.”
Treat indoor mold growth of any kind as something to be corrected. -
Focus on finding and removing mold growth, not chasing lab labels.
Methods like Wall Check / cavity sampling can directly answer: “Is there mold growing inside this wall?” - If you can’t afford advanced testing, the simplest test is experiential: You leave or move temporarily. You notice whether you feel better in a different environment
-
Be cautious with trendy “mushroom” products.
Mushrooms can be helpful (vitamin D, medicinal compounds, antibiotics like penicillin historically) and also sources of toxins and heavy metals, especially if collected outdoors or processed without good quality control. - More is not always better just because it’s labeled “natural” or “functional.”
Key Takeaways
-
All molds have the potential to produce mycotoxins.
“Toxic mold species” vs “safe mold species” is an oversimplification. -
Mycotoxins are secondary metabolites.
They are not always present. Their production depends on environment and stress. -
You cannot reliably trace a mycotoxin in urine back to a specific mold in your house.
Food, environment, detox capacity, and lab variability blur the picture. -
For health and home decisions, the core question is still:
“Is there actual mold growth in this building, and can we remove it?” -
Don’t let the word “mycotoxin” distract you.
It’s more important to address moisture and mold growth, improve your environment overall, and work with practitioners who see the whole picture, not just a lab panel.
Don’t get stuck on the word mycotoxin and think you can evaluate the connection between your health and your house based on it. You can’t. Focus on whether there is actual mold growth in your home, and if so, where it is, and how to eliminate it.
Stay curious, stay skeptical, and most importantly—if you have mold, focus on finding it and fixing it, not chasing labels.
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Disclaimer
The post is designed for educational purposes only. Our goal is to provide information and scientific data as to the potential hazards in the home or office. All the factors to be considered are beyond the scope of this post. We do not assume responsibility for choices or decisions made including those regarding mitigation. The principles presented here should empower the reader to make informed choices. Book a consultation.