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The Bad Stuff in Mold (It’s Not Just Toxins)

A common misconception is mold toxins are the most dangerous indoor biological air pollutant. As the name suggests, fungal mycotoxins are indeed toxic. But the health hazard from indoor mold is caused by multiple mold elements. Many fall into a class of compounds called inflammagens—inflammation-inducing particles.

According to the World Health Organization:

“Microbial growth may result in greater numbers of spores, cell fragments, allergens, mycotoxins, endotoxins, β-glucans and volatile organic compounds in indoor air. The causative agents of adverse health effects have not been identified conclusively, but an excess level of any of these agents in the indoor environment is a potential health hazard.”

This article will discuss mycotoxins and other dangerous components of mold.


Spores are the seeds of the fungal world—tiny reproductive units that travel through the air. When the drifting spores chance upon suitable conditions, they can settle and grow, resulting in a mold infestation.

Spores require two conditions to grow: a food source and moisture.

In a typical home, food sources abound. One indoor environmental professional quipped that standard building materials are “mold food”—the cellulose in wood and the gypsum board in drywall are among the carbon-based substates that mold thrive upon.

Spores are the main component of mold that will cause an infection. The other components listed below cannot readily reproduce and spread within the human body.

Aspergillosis, caused byAspergillus mold, and Valley Fever, caused by the round mold Coccidiodes, are examples of infections—both typically start with pneumonia but, untreated, can spread to the blood and, from there, to the brain and central nervous system.

Cell Fragments

Cell fragments are small pieces of mold spores or other mold structures. Cell fragments outnumber spores by a factor ofat least 300 to 1. While they do not cause an infection—like spores do—cell fragments can cause massive immune problems including innate immune activation, immune suppression, and autoimmunity.

Inhaled cell fragments damage the immune system because the immune system can detect foreign material on the mold. Protein detectors on immune cells, known as pattern recognition receptors, recognize danger signals on mold. Triggering danger signals on mold—known as Pathogen-Associated Molecular Patterns and Damage-Associated Molecular Patterns—cause the damaging inflammatory response.


Mold is a common allergen. Allergy is a widely accepted mold injury mechanism and allergen-inducing elements of mold include the fungal cell wall, which is composed of complex sugar particles known as polysaccharides.


Mycotoxins are toxic metabolites produced by mold. They can cause disease and death in human, as well as other animals. Mycotoxins can cause acute or chronic illness. According to microbiologist J.W. Bennett,

“Almost certainly, the main human and veterinary health burden of mycotoxin exposure is related to chronic exposure.”

There are hundreds of identified mycotoxins, each with different effects on health. To give but three examples:

  • Aflatoxins, made by Aspergillus, is toxic and can be cancer-inducing. The greatest risk is to the liver, a center of detoxification that may become overwhelmed.
  • Citrinin, made by Penicillium, is toxic to the kidney in all animal species tested.
  • Trichothecenes are produced by numerous molds, most notably Stachybotrys, and damage protein production.


Endotoxins are made by gram-negative bacteria, not mold. They may be found along with mold and can cause a strong immune response, including fever and shock.


Beta-glucans are a major component of the mold cell wall. This polysaccharides makes up more than half of the dry weight of the call wall. A high level of beta-glucans may cause allergic disease and innate immune activation.

Volatile organic compounds

Volatile organic compounds (VOCs) are noxious gasses that evaporate into the air. Mold produces these noxious gasses, which is a source of the musty odor found within water-damaged buildings. Geosmin is an example of one such toxic gas produced by mold. By direct contact, microbial VOCs can cause eye and nasal irritation. When inhaled, they can also contribute to headaches, asthma, infertility, and fatigue. VOCs drive chronic inflammation, including innate immune activation and autoimmunity.