What is Toxic Mould? and Why It Affects Some People More Than Others
Mould. Most of us think of it as something unpleasant to look at or something that smells a bit off — usually hiding in a bathroom corner or the back of a cupboard. But for some people, mould is far more than a nuisance. It can be the invisible trigger behind brain fog, fatigue, chronic illness, skin issues, and behavioural changes in children.
So why does mould make some people sick and not others? And why are many standard tests unable to detect the root cause?
The answers lie in a combination of toxic mould, environmental exposure, and your unique genetic makeup.
What Is Mould?
Mould is a type of fungus that grows in damp, warm, and poorly ventilated environments. It spreads by releasing microscopic spores into the air — spores that can land on walls, clothes, furniture, and even travel through your home’s ducted heating or air conditioning.
Not all moulds are dangerous. However, certain species produce mycotoxins — toxic compounds that can disrupt the body’s natural systems. This is what people refer to as toxic mould.
What Makes Mould Toxic?
Toxic mould releases substances called mycotoxins, which are invisible and odourless but can deeply affect the body. When inhaled or absorbed through the skin, mycotoxins can:
Overload your immune system
Damage your gut lining
Interfere with your brain’s chemistry
Trigger inflammation
Suppress detoxification pathways
Mimic or disrupt hormones
For some people, exposure to toxic mould causes mild sinus symptoms or fatigue. For others, it leads to debilitating illness, misdiagnosis, and years of unexplained health problems.
Common Types of Toxic Mould – and What They Can Do
| Mould Type | Where It’s Found | Possible Symptoms |
|---|---|---|
| Stachybotrys chartarum (Black mould) |
Behind walls, ceilings, insulation, wallpaper after flooding or leaks | Fatigue, memory loss, breathing issues, skin irritation, mood swings, brain fog |
| Aspergillus | Air conditioners, ducted heating, insulation, dust | Iron deficiency, lung infections, fatigue, sinus issues, gut symptoms |
| Penicillium | Carpets, mattresses, water-damaged fabrics, insulation | Chronic congestion, asthma, fatigue, bloating |
| Chaetomium | Damp drywall, wallpaper, under floorboards | Brain fog, blurred vision, tingling, sinus pain |
| Fusarium | Bathrooms, wet carpet, pot plants | Digestive upset, nausea, skin issues, immune suppression |
| Cladosporium | Damp wood, fabrics, curtains, windows | Cough, asthma, eczema, hay fever-type symptoms |
These moulds often go unseen. Even a clean-looking home may still have dangerous levels of mould behind walls or under flooring, especially after water damage.
Why It Affects Some People More Than Others
One of the most confusing aspects of mould illness is that not everyone gets sick — even if they’re living in the same environment. This comes down to genetic susceptibility.
Some people have genetic traits that make it harder for their bodies to detoxify and clear mould toxins. Instead of eliminating the toxins efficiently, their immune system struggles to recognise them — allowing toxins to build up and cause inflammation over time.
The Role of Genetics in Mould Sensitivity
The most commonly implicated genes in mould-related illness include:
HLA-DR: Impairs the immune system’s ability to recognise mould toxins, making it harder to eliminate them.
MTHFR: Affects methylation and detoxification, leading to poor clearance of environmental toxins.
COMT: Affects stress response and detox of neurotransmitters.
DAO and HNMT: Involved in breaking down histamine, often disrupted in mould-sensitive individuals.
CYP and GST genes: Affect liver detox pathways.
Around 25% of people carry the HLA-DR “mould susceptible” genotype. Without knowing this, symptoms can seem random, unexplained, or even psychological.
How Toxic Mould Triggers Strange, Overlooked Symptoms
While some symptoms of mould illness seem obvious (like coughing or sinus pressure), many are less well-known — especially in genetically susceptible people.
1. Iron Deficiency That Doesn’t Respond to Supplements
Some moulds (like Aspergillus) survive by extracting iron from their host — including from saliva. This deprives your body of usable iron, leading to:
Pale skin
Chronic fatigue
Brittle nails
Restless legs
Mouth sores
Hair thinning
Breathlessness
Traditional iron supplements often don’t help unless the mould is dealt with first.
2. Sudden Food Sensitivities & Histamine Reactions
Mould can damage the gut and reduce DAO enzyme activity — causing histamine intolerance, where even healthy foods can trigger symptoms.
Common signs include:
Hives, itching, or rashes
Anxiety after eating
Headaches from leftovers, wine, cheese
Congestion or post-nasal drip
Flushing or rapid heart rate
3. Hormonal Imbalances
Mycotoxins can mimic oestrogen, interfere with detox, and suppress hormone production — leading to:
Worsening PMS
Irregular periods
Infertility
Hormonal acne
Low libido
Breast tenderness
Men may also experience testosterone drop, fatigue, and poor motivation.
4. Neurological + Behavioural Shifts
Toxic mould can cross the blood-brain barrier, affecting neurotransmitters. This may cause:
Mood swings
Brain fog
Anxiety or panic attacks
ADD/ADHD symptoms
Speech regression in children
OCD behaviours or emotional sensitivity
5. Gut + Immune Dysfunction
Mould can impair digestion, inflame the gut lining, and trigger overgrowths like candida or SIBO. Symptoms may include:
Bloating or gas
Constipation or diarrhoea
White tongue coating
Cravings for sugar
Constant illness or infections
Low tolerance to supplements or medications
6. Autoimmune-like Flares
Mould exposure can mimic or worsen autoimmune conditions like:
Psoriasis
Lupus
Hashimoto’s thyroiditis
Chronic fatigue syndrome
Fibromyalgia
POTS (Postural Orthostatic Tachycardia Syndrome)
These symptoms may wax and wane, and often worsen after physical or emotional stress.
7. Persistent Respiratory + Sinus Issues
Mycotoxins often attack the respiratory tract, causing:
Chronic sinus infections
Coughing
Shortness of breath
Wheezing
Loss of smell
Asthma flares in adults or children
Even after leaving the environment, symptoms may linger if toxins are still stored in the body.
How Mould Exposure Happens (Even If You Don’t See It)
You don’t need to see visible black patches to be exposed to mould. Mycotoxins and spores can come from:
Water leaks in ceilings or under sinks
Poorly ventilated bathrooms or kitchens
Mould inside mattresses, prams, and couches
Homes built without adequate damp-proofing
Ducted heating or split systems that circulate spores
Buildings with previous flooding, plumbing issues, or storm damage
A “clean” house can still have dangerous levels of airborne mould particles — especially in older buildings.
Why Standard Medical Tests Often Miss Mould Illness
Mainstream blood tests usually don’t detect mould exposure. For example:
Iron deficiency may show up, but the cause is missed
Liver enzymes may appear normal, even if detox is impaired
Histamine intolerance is rarely tested
Inflammation markers may be mildly raised but non-specific
Allergy tests may be negative (because the issue is inflammatory, not allergic)
Without looking deeper — into genes, mycotoxin levels, or environmental history — many people are misdiagnosed or dismissed.
Who Is Most at Risk?
While mould can affect anyone, certain groups are more vulnerable:
People with HLA-DR or detox gene variations
Infants and young children
Pregnant or breastfeeding women
Those with autoimmune conditions
People with past trauma or chronic stress (impacts detox and immune response)
Those with a history of antibiotic or steroid overuse
Anyone living or working in a previously flooded or damp building
Even pets can develop symptoms when exposed long-term.
What Happens Inside the Body During Mould Exposure?
Here’s a simplified overview:
Exposure: You inhale or absorb mould toxins.
Immune Confusion: If you’re genetically susceptible, your body doesn’t recognise or eliminate the toxins.
Inflammation: Toxins circulate, triggering ongoing immune activation.
Breakdown: Systems like your gut, brain, hormones, and liver become overwhelmed.
Symptoms Begin: These can vary depending on your genetics, past health history, and current environment.
Mould, Histamine, and MCAS — How They’re Connected
| Condition | Triggered By | Common Symptoms |
|---|---|---|
| Histamine Intolerance | Low DAO enzyme, gut damage | Rashes, flushing, anxiety, fatigue |
| MCAS (Mast Cell Activation Syndrome) | Immune overstimulation | Itching, brain fog, sensitivities, gut issues |
| CIRS (Chronic Inflammatory Response Syndrome) | Biotoxin exposure | Memory issues, fatigue, pain, multi-system illness |
Many people affected by mould find they eventually react to foods, smells, supplements, light, or even sound — often due to mast cell activation and histamine overload.