23/10/2026
Mould: what you need to know
A while back I asked what people wanted to learn about, and mould toxicity was one of the responses. It is a large topic, so I do have three posts planned to tackle this.
It’s also a timely topic as it is spring in New Zealand, particularly in Northland where I live where it can be very wet.
Mould is found everywhere in our world. Moulds and fungi survive and grow by breaking down organic material. This is fantastic when it is dead and decaying matter in the garden - they return nutrients to the soil so they can be taken up by plants. However, when they are growing inside, in our homes, schools, or workplaces it can have a serious negative effect on our health.
Mould grows in thin strings of cells, called hyphae. They reproduce by releasing microscopic spores into the air. These are found almost everywhere, and can resist extremes of temperature, and stay dormant until the right conditions come along for them to grow. Mould needs moisture, a food source (something organic) and a suitable temperature - not too cold.
Unfortunately that makes Northland a prime area for mould growth at any time, and flooding, followed by the humidity we had afterwards is a prime driver for mould growth.
Even without the flooding, areas in the house can also be a good area for mould growth. Particularly bathrooms and kitchens, rooms with inadequate air flow, and the crawl space below the house.
Relative humidity above ~60% significantly increases the likelihood of mould growth (WHO, 2009).
Indoor moulds vary widely, but commonly identified genera include:
* Aspergillus
* Penicillium
* Cladosporium
* Stachybotrys chartarum (often referred to as “black mould”)
Different species have different health implications, though identification is not always necessary for risk management.
While mould itself can trigger allergic and respiratory symptoms, some species produce mycotoxins, compounds that have attracted increasing attention for their potential role in human health.
Mycotoxins are secondary metabolites produced by certain fungi. They are useful for protecting the organism from competition. While not a mycotoxin, a well known secondary metabolite produced by a mould is Penicillin. This substance kills bacteria - so while not toxic to humans (unless you have an allergy!), it is most certainly toxic to bacteria.
Some well-known mycotoxins include:
* Aflatoxins
* Ochratoxin A
* Trichothecenes
* Fumonisins
The problem with these is they can persist in the environment. This means that water damaged areas, that have mould growth which later dries, can have a large concentration of these dried mycotoxins, which are just as dangerous when dried and inhaled as they are when the mould is fresh and growing.
However, we can also find mycotoxins in other places. Food contamination is well known - and has been happening for hundreds of years. It is considered possible that ergot contamination of rye was responsible for the hallucinations and hysteria that led to the Salem witch trials in 1692. These days we are most likely to find mycotoxins in grains such as corn and wheat, nuts (particularly peanuts), coffee and dried fruit such as prunes, dates and raisins.
The real problem with mycotoxins is the way they can insidiously make their way throughout the body. They are molecules that are both lipophilic (fat loving), and hydrophilic (water loving), which makes them easily pe*****te different parts of the body. The mycotoxins can enter cells, and cause a cascade of biological processes and set off a strong inflammatory process.
So why do some people get sick from Mould and mycotoxins and others don’t?
Individual susceptibility varies and can be down to a range of things.
* Genetic differences can influence the ability to metabolise and excrete mycotoxins
* Stress, nutrition and other lifestyle factors can also influence how the body clears mycotoxins.
* Type and length of exposure
* Other illnesses or immune dysregulation
Dr Neil Nathan estimates that up to 25% of people cannot easily clear mycotoxins, which means the inflammatory process persists.
Mould can have a serious adverse effect on your health. The WHO acknowledges there is an Increased risk of respiratory symptoms, including an exacerbation of asthma, allergic rhinitis, and coughing and wheezing.
However, there are a large range of other symptoms that can also be seen with mould and mycotoxins. These can include fatigue, weakness, muscle aches and cramps, headaches, sensitivity to bright lights, abdominal pain, nausea and diarrhoea, skin sensitivity to light touch, numbness and tingling, sensitivity to electrical shocks or unusual pains, and for women, heavy periods (Nathan, N. 2009).
Mycotoxins can also cause liver toxicity from aflatoxins, kidney damage from ochratoxin A, and immune suppression.
Mould can also be a contributing factor to conditions such as Mast Cell Activation Syndrome (MCAS) and Pediatric Acute-onset Neuropsychiatric Syndrome (PANS). Chronic Inflammatory Response Syndrome (CIRS) can also be caused by mould.
Casual mould exposure doesn’t affect everyone (but prolonged mould exposure is likely to have a deleterious effect on your health). People who are immunocompromised, have existing allergies or asthma, and those who are very young or very old are at greater risk. Repeated exposures, poor health, and stress can also affect your susceptibility.
Prevention of mould growth is easier and better than remediation. The main ways to do this include:
Keeping your indoor humidity low - below 50% ideally
Use extractor fans in kitchens and bathrooms
Repair leaks as soon as you find them
Ensure insulation and air flow
Clean small amounts of visible mould as soon as possible
If you can see water damage, visible mould or smell that musty mould odour, the time to act on it is now, before mould gets a bigger foothold or causes any health problems.
References
* World Health Organization (2009). WHO Guidelines for Indoor Air Quality: Dampness and Mould.
* Nathan, N. (2009). Toxic: Heal Your Body from Mold Toxicity, Lyme Disease, Multiple Chemical Sensitivities, and Chronic Environmental Illness. Victory Belt Publishing Inc.
