Deep dive #6 · 9 November 2026

Mould exposure and health

For health professionals General practice

Damp homes make airways worse: that part is settled. A whole industry now sells something bigger: urine tests, "biotoxin" protocols and a syndrome with no agreed definition. The patients in front of us are genuinely unwell either way. Here is what the evidence supports, what is still hypothesis, and what is marketing.

At a glance

Established: damp and mould are linked with cough, wheeze, upper airway symptoms, respiratory infections and asthma flares (IOM 2004, WHO 2009). New asthma: OR 1.29 with visible mould, 1.73 with mould odour (Quansah 2012).
Specific diseases: hypersensitivity pneumonitis (uncommon), ABPA in asthma or CF, and invasive fungal disease in the immunocompromised.
Australia: 27% of renters report mould and 21% damp (Australian Rental Housing Conditions Dataset).
Mycotoxins: real toxins when eaten (aflatoxin). Inhaled at indoor doses, harm is not shown (ACMT 2025).
"CIRS": "not a recognised disease in Australia, with no scientifically validated or approved diagnostic criteria" (Australian Government clinical pathway, 2023).
Fix: find and stop the water, clean or remove mould, and treat the disease in front of you. Repairs cut adult wheeze (OR 0.64; Cochrane 2015).

Biggest take-home: the most useful mould test is a torch and a moisture source, not a urine sample.

For patients, in one line: damp and mould can trigger asthma, hay fever-like symptoms and, rarely, serious lung problems, so fix the moisture and see your GP if you're unwell. Read the plain-English mould page.

Definition

Dampness: visible water damage, damp patches, condensation or a musty smell. WHO treats dampness and mould as one exposure, because the moisture drives many microbes at once.
Mould: filamentous fungi that release spores, hyphal fragments, microbial volatile organic compounds (the smell) and, for some species, mycotoxins.
Mould-related illness (evidence-based use): allergic, irritant, hypersensitivity or infectious disease with plausible exposure.
"Mould illness" or "CIRS" (commercial and advocacy use): a proposed chronic multisystem syndrome attributed to "biotoxins". No validated criteria exist.

History

1932, John Munro Campbell: "Acute symptoms following work with hay": the description now recognised as farmer's lung, a hypersensitivity pneumonitis.
1943, Mary Hunt (Peoria, US): credited, in the best-known account, with the mouldy cantaloupe whose Penicillium strain fed wartime penicillin production. USDA historians note the record is uncertain.
1950, Elizabeth Lee Hazen and Rachel Fuller Brown: discovered nystatin, the first widely used antifungal, from soil in a friend's garden.
1952, Hinson, Moon and Plummer: described broncho-pulmonary aspergillosis in Thorax (8 new cases), the start of ABPA as a diagnosis.
1960, England: about 100,000 turkeys died of "turkey X disease" from Aspergillus flavus-contaminated Brazilian groundnut meal: aflatoxin was named.
1994–2000, Cleveland: 10 infants with pulmonary haemorrhage were linked to Stachybotrys; CDC's 2000 review called the association "not proven".
2004 and 2009: the Institute of Medicine and WHO set the evidence base for damp and health.
2018–2024: Australia's parliamentary inquiry reports (October 2018); the government responds (March 2020); Ritesh Agarwal's group in Chandigarh, India, leads revised international ABPA guidelines (2024).

Pathophysiology

Five mechanisms are established. The sixth, systemic toxicity from inhaled mycotoxins, is not.

Allergy (type I): fungal allergens drive IgE sensitisation, rhinitis and asthma onset or flares.
Irritant and innate inflammation: fungal cell wall components and microbial volatiles irritate airways in non-allergic people: cough, wheeze, upper airway symptoms (IOM "sufficient evidence").
Hypersensitivity pneumonitis: repeated inhalation in susceptible people triggers an immune response in small airways and alveoli. The ATS/JRS/ALAT guideline splits it into non-fibrotic and fibrotic types.
ABPA: Aspergillus persists in airways of people with asthma or CF and drives an intense IgE and IgG response, eosinophilia and bronchiectasis.
Invasive disease: in neutropenia, transplant, ICU, COPD or lung cancer, Aspergillus invades tissue.
Mycotoxins: toxic when ingested in food (aflatoxin causes liver cancer). Indoors, they are non-volatile, and modelled inhaled doses are far below harmful thresholds (ACMT 2025).

How damp and mould affect health: five established pathways and one unproven one (after IOM 2004, WHO 2009, ACMT 2025). Download this diagram

Epidemiology

Global

Exposure: dampness affects an estimated 10–50% of indoor environments in Europe, North America, Australia, India and Japan (WHO 2009).
Asthma burden: damp and mould raised respiratory and asthma outcomes by 30–50% (Fisk 2007 meta-analysis). About 21% of current US asthma, 4.6 million cases, was attributed to home damp and mould (Mudarri and Fisk 2007).
Fungal disease (Denning 2024): about 2.1 million people a year develop invasive aspergillosis, with crude mortality of 85.2%. Fungal asthma affects about 11.5 million people and may contribute to 46,000 asthma deaths a year.
ABPA: 28% of people with asthma were Aspergillus-sensitised and 12.9% had ABPA in a 2009 meta-analysis of mostly specialist series, with wide variation in criteria.

Australia

Renters: 27% report mould and 21% dampness (Australian Rental Housing Conditions Dataset, over 14,000 households).
"CIRS": "There is no reliable evidence on the clinical epidemiology of CIRS" in Australia (clinical pathway, 2023).

Causes and risk factors

Moisture sources: roof and plumbing leaks, floods, rising damp, condensation from cooking, showers and drying clothes indoors, and poor ventilation.
Housing: WHO advises prioritising remediation in poorly maintained low-income housing.
Higher-risk people: asthma, allergies or other breathing conditions; weakened immunity or chronic lung disease (risk of mould infection) (NSW Health).
Occupational: farmers and others handling mouldy hay, grain or compost (hypersensitivity pneumonitis).
Ingestion, not inhalation: aflatoxin-contaminated food is the main real-world mycotoxin risk worldwide.

Preventable factors

Dry within 24–48 hours: mould often won't grow if wet materials dry this fast (EPA).
Indoor humidity: keep below 60%, ideally 30–50% (EPA). A hygrometer is cheap.
Ventilate: exhaust fans in bathrooms and kitchens; don't dry clothes indoors without ventilation.
Repair fast: repairs improve symptoms (Cochrane 2015). England now has legal timeframes for social landlords (Awaab's Law, from 27 October 2025).
Building codes: Australia's National Construction Code added condensation provisions from 2019 (Australian Government response, 2020).

Diagnosis essentials

In general practice

Take an exposure history: home, work and leisure; when it started; whether symptoms ease away from the building (clinical pathway 2023).
Examine: eyes, upper airways, chest and skin. Most damp-related symptoms show up there.
Test for what you can treat: spirometry with bronchodilator (asthma per the Australian Asthma Handbook), FBC with eosinophils, total IgE, and mould-specific IgE or skin prick testing.
Exclude other causes of fatigue, cognitive symptoms and pain, and treat what you find.
Advise on exposure whether or not you find a disease, and give written advice (the pathway recommends the enHealth fact sheet).
Refer: respiratory physician for respiratory disease; clinical immunology or allergy for sensitisation questions; paediatric review for infants with significant wheeze.

Specific diagnoses

ABPA (ISHAM 2024): predisposing condition or compatible picture, plus fungal sensitisation and total IgE ≥500 IU/mL, plus 2 of: fungal-specific IgG, blood eosinophilia, suggestive imaging. Screen newly diagnosed adult asthma with fungus-specific IgE in tertiary care.
Hypersensitivity pneumonitis (ATS/JRS/ALAT 2020): structured exposure history, HRCT, serum IgG to identify exposures, and BAL lymphocytes. Specialist-led.
Invasive aspergillosis: suspect in the immunocompromised with new lung lesions; urgent specialist care.

Tests that don't help

Urine mycotoxins: no FDA-approved test exists; mycotoxins appear in healthy people's urine, and no level predicts disease (CDC MMWR 2015).
Serum mycotoxins, cytokines, eosinophil cationic protein: "not recommended" (clinical pathway 2023).
Mould IgG for allergy: "of no diagnostic relevance" (pathway). IgG has a role only in hypersensitivity pneumonitis and ABPA.
Visual contrast sensitivity (VCS): used in CIRS protocols; not a validated test for exposure or disease.
Home mould species testing: if you can see it, remove it; the species doesn't change the advice (CDC, EPA, NSW Health). EPA does not recommend routine ERMI testing.

A positive urine mycotoxin result doesn't tell you where the exposure came from, or that it caused anything.

The CIRS and Shoemaker claims, appraised

What's claimed: a genetically susceptible person exposed to a water-damaged building develops chronic multisystem inflammation, diagnosed with VCS, HLA typing and a biomarker panel, and treated with cholestyramine and VIP nasal spray.
The core study (Shoemaker and House 2006): 28 patients, 26 completers; a 2-week placebo-controlled cholestyramine phase in 13 (7 vs 6). Symptoms fell from 23 to 4 of 37. Small, short, single group, not independently replicated.
Australian inquiry: the House of Representatives "Report on the Inquiry into Biotoxin-related Illnesses in Australia" (October 2018) found the CIRS–biotoxin link "difficult to determine" without clinical guidelines. It recommended a fact sheet, research funding, mould testing and remediation standards, better tenant disclosure and repair, building code review and GP clinical guidelines.
Response: the government (March 2020) accepted most recommendations. NHMRC funded one grant ($1.06 million, Macquarie University, 2022–25). The resulting clinical pathway (November 2023) classifies CIRS as having "insufficient or inadequate evidence of association" with damp or mould.
Treatment harms: cholestyramine causes abdominal pain, nausea, diarrhoea and constipation. VIP nasal spray isn't on the ARTG; pancreatitis and depression have been described (pathway appendix).
Kind framing: the symptoms are real. Saying "this label isn't supported" is not saying "you're not unwell". Patients often arrive having paid a lot already.

Current treatment

Remove the exposure: remediation of damaged houses reduced adult wheeze (OR 0.64, 95% CI 0.55–0.75) and rhinitis (OR 0.57, 0.49–0.66). In children, no clear difference from information alone. 12 studies, 8,028 people, very low to moderate quality (Cochrane 2015).
Cleaning (CDC, EPA, NSW Health): under about 10 square feet (roughly 1 m²), most people can clean it themselves. Use detergent or diluted vinegar; for stubborn mould, bleach no stronger than 1 cup per gallon (NSW: 250 mL in 4 L). Never mix bleach with ammonia. Wear an N95 or P2 mask, gloves and goggles. Throw out porous items that stay wet.
Bigger jobs: heavy water damage or hidden mould: a professional, and the landlord if renting.
Asthma and rhinitis: usual stepwise care, plus exposure control.
ABPA (ISHAM 2024): prednisolone or itraconazole monotherapy for acute disease; combine them only for recurrent exacerbations. In an RCT of 191 patients, adding itraconazole to prednisolone gave 20.6% vs 33% exacerbations at 1 year (p=0.054).
Fungal-sensitised severe asthma (FAST): itraconazole improved asthma quality of life by 0.85 points vs −0.01 on placebo (n=58); 5 of 7 discontinuations for adverse events were in the itraconazole arm.
Hypersensitivity pneumonitis: identify and avoid the antigen; specialist management.
Persistent unexplained symptoms: the pathway recommends person-centred, stepped care with a time-bound plan, regular review and multidisciplinary input, and avoiding repeated testing and unvalidated treatments.

Emerging treatments and trials

ABPA sequencing: the 2022 RCT authors call for a 3-arm trial of prednisolone vs itraconazole vs both.
Australian CIRS research: NHMRC's one targeted grant aimed at "an integrated platform for the early diagnosis and treatment of biotoxin-related illnesses". We did not find published outcomes when we checked.
Housing law as treatment: Awaab's Law (England) requires social landlords to investigate significant damp and mould within 10 working days and act on serious risks within 5. No health outcomes yet.

Theoretical frontiers

Hypotheses, not recommendations.

Causes: theories

Hypothesis: the smell marks the culprit. Mould odour carried a higher asthma onset estimate (1.73) than visible mould (1.29), and water damage alone wasn't significant (1.12; Quansah 2012). Against: odour is self-reported, and studies were heterogeneous. Test: a birth cohort with measured microbial volatiles and DNA-based fungal sampling.
Hypothesis: inhaled mycotoxins cause multisystem illness. For: toxigenic moulds grow indoors, and toxins harm cells and animals (IOM 2004). Against: non-volatile, modelled doses far below harmful levels (ACMT 2025); urine positives in healthy people (CDC 2015). Test: blinded case–control study using validated home exposure measures and validated biomarkers.
Hypothesis: "CIRS" is an innate immune syndrome in genetically susceptible people. For: symptom and VCS change with cholestyramine in 26 completers (Shoemaker 2006). Against: no validated criteria, no reliable epidemiology (pathway 2023). Test: pre-registered case–control study with a blinded biomarker panel and independent replication.
Hypothesis: it's the whole damp microbiome, not mould alone. For: WHO treats dampness-related microbes as one exposure and sets no microbe thresholds. Against: mould markers outperform water damage for asthma onset (Quansah). Test: metagenomic sampling of bacteria, endotoxin and fungi in cohorts.
Hypothesis: microbial diversity protects; damp distorts it. For: diverse farm microbes lowered asthma odds (OR 0.62 and 0.86), and one fungal taxon, Eurotium, 0.37 (Ege 2011). Against: cross-sectional; farms aren't damp homes. Test: birth cohort comparing diversity with damp-associated taxa.
Hypothesis: attribution amplifies symptoms. For: after one positive urine test, coworkers began attributing their own symptoms to mould in a building with no damp (CDC 2015). Against: anecdote; can't explain objective disease. Test: blinded exposure-chamber provocation study.

Prevention: theoretical options

Hypothesis: legal repair timeframes prevent disease. For: repairs reduce wheeze (Cochrane OR 0.64). Against: no health data from Awaab's Law yet. Test: interrupted time series of child respiratory admissions in English social housing.
Hypothesis: condensation rules in building codes cut asthma. For: condensation is a major moisture source; NCC provisions from 2019. Against: no health evaluation found. Test: compare mould and asthma rates in homes built before and after.
Hypothesis: a $10–50 hygrometer is an asthma intervention. For: EPA's 30–50% humidity target. Against: no trial. Test: cluster RCT of humidity monitors plus feedback in rentals.
Hypothesis: targeted remediation in low-income housing reduces inequity. For: WHO prioritises it; 27% of Australian renters report mould. Against: children didn't clearly benefit in Cochrane. Test: a randomised remediation programme with ED visits as the outcome.
Hypothesis: screening asthma for fungal sensitisation finds ABPA earlier. For: ISHAM 2024 recommends it in tertiary care. Against: primary care yield unknown. Test: a primary care screening study with treatment outcomes.

Treatment: theoretical options

Hypothesis: antifungals help fungal-sensitised severe asthma. For: FAST (+0.85 quality of life). Against: n=58, adverse events. Test: a larger RCT with exacerbations as the primary outcome.
Hypothesis: itraconazole first spares steroids in ABPA. For: ISHAM allows either; combination trended better (p=0.054). Against: no head-to-head monotherapy trial. Test: the 3-arm RCT the trialists propose.
Hypothesis: cholestyramine treats "biotoxin illness". For: Shoemaker 2006 (13 randomised). Against: tiny, 2 weeks, unreplicated, GI adverse effects. Test: an independent, adequately powered, blinded RCT with patient-centred outcomes.
Hypothesis: VIP nasal spray restores regulation. For: used in CIRS protocols. Against: not on the ARTG; no RCT found; adverse effects described. Test: a placebo-controlled phase 2 trial.
Hypothesis: stepped multidisciplinary care beats the protocol route. For: recommended by the pathway for persistent unexplained symptoms. Against: no trial in people attributing illness to mould. Test: a pragmatic RCT in general practice.
Hypothesis: remediation is treatment for children too. For: adult benefit. Against: no clear child benefit yet. Test: a cluster RCT in children with asthma.

Gaps and open questions

No dose–response thresholds: WHO could not recommend any microbial level as safe.
Exposure measurement: most studies rely on reported damp or smell.
Persistent multisystem symptoms: real, disabling and unexplained, with no trial-tested care pathway.
Australian data: mould is common in rentals, but we found no Australian cohort linking measured exposure to disease.
Paediatric remediation: adult benefit, unclear child benefit.

Prognosis and quality of life

Asthma and rhinitis: improve after repairs (adult wheeze OR 0.64).
ABPA: responds well to treatment. In the 2022 RCT, all 191 responded at 6 weeks, and none became steroid-dependent within 24 months.
Invasive aspergillosis: crude mortality 85.2% worldwide, including untreated cases (Denning 2024).
People labelled with "CIRS": outcomes unknown; costs of testing and protocols can be high, and one workplace case cost a building manager over US$25,000 in destructive testing (CDC 2015).

Weird trivia

Nystatin is named after New York State, where Hazen and Brown worked.
Aflatoxin is a contraction: Aspergillus flavus toxin.
Salem, 1692: psychologist Linnda Caporael proposed in Science (1976) that ergot-contaminated rye fuelled the witch trials. It remains a hypothesis.
"Mouldy Mary": the cantaloupe story is famous; USDA historians say three different people have been credited.
Farmer's lung was first written up under the plain title "Acute symptoms following work with hay".
Awaab's Law is named after Awaab Ishak, a 2-year-old whose death a coroner linked to prolonged mould exposure in his rented home.

Guidelines

Key trials

Shoemaker and House 2006 (Neurotoxicol Teratol): the cholestyramine CIRS study; 13 randomised for 2 weeks.
Fisk 2007 (meta-analysis): damp and mould raise respiratory outcomes by 30–50%.
FAST 2009 (AJRCCM): itraconazole in fungal-sensitised severe asthma.
Ege 2011 (NEJM): microbial diversity protects against asthma.
Quansah 2012 (PLoS One): damp and mould predict new asthma.
Cochrane 2015 (Sauni): remediation reduces adult wheeze and rhinitis.
Agarwal 2022 (Eur Respir J): prednisolone ± itraconazole in ABPA, n=191.

Sources

Information only. Follow the Australian Asthma Handbook, specialist advice and local referral pathways. Don't order unvalidated mycotoxin or CIRS panels.

Updated 9 November 2026. General education for health professionals; not a substitute for local protocols.

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