In the airways, yes. Mold parts can break into the lining of your nose and lungs and set off alarm signals that drive allergic inflammation, and damp, moldy homes are firmly linked to asthma and allergies. Inflammation in the rest of the body is far less clear. It rests on one study of 291 children.
Mold is already in the air you breathe. Fungi live everywhere, outdoors and indoors, and many make spores small enough to inhale. Most of the time your airways clear them quietly.
A damp home changes that. In a 2025 study of lung patients in Texas, home mold mostly came from water that kept getting in, and it turned up most often in the bathroom, the bedroom and the air conditioner. Our [guide to indoor mold and your health](/articles/how-indoor-mold-affects-your-health) covers what living with it does to breathing, sleep and mood. This part goes one level down. What happens inside you, step by step? And where does the science stop?
What's happening in the body
First contact: the lining of your airways
Your nose, throat and lungs are lined with a thin layer of cells, which works like a wall with an alarm wired into it.
Mold is built from parts the lining knows how to spot. Its cell walls hold molecules called beta-glucan and chitin, and it releases enzymes called proteases. Cells in the lining, along with immune cells called dendritic cells, carry sensors that react to these parts by releasing inflammation signals. One sensor, Dectin-1, recognizes the fungal cell wall. It helps protect you from fungi. It may also play a part in severe asthma.
The alarm: when the barrier is breached
The proteases are the troublemakers. A 2026 review explains that fungal proteases can break down the airway's barrier and trigger receptors in the lining, which then releases alarm signals with names like IL-25, IL-33 and TSLP. Those alarms call in immune cells, including mast cells and eosinophils (white blood cells common in allergy). What follows is more mucus, airways that tighten too easily, and over time, changes to the airway tissue.
This is called type 2 inflammation. It is the kind behind allergic asthma. Two molds, Alternaria and Aspergillus, are the main fungal allergens known to set it off.
Allergy: when the body learns to overreact
Some immune systems learn to react to mold. Doctors call that being sensitized. Molds do this less often than many other allergens, and about 3 to 10% of people in Europe are sensitized. When it happens, though, it can matter. Asthma and long-lasting sinus trouble tied to fungal allergy tend to be more severe. And fungal sensitization is common in severe asthma.
Deep in the lungs: hypersensitivity pneumonitis
A rarer reaction happens deeper, in the smallest airways and the lung tissue. It is called hypersensitivity pneumonitis (HP): an immune response that runs far too hot after someone sensitized breathes in a trigger, most often from birds or fungi. The long-lasting kind usually comes from low-level exposure over a long time, often to birds or molds in the home.
How common is mold as the trigger? At one Texas lung center, home mold was named as the trigger in 54 of 231 people with HP.
Infection: rare in healthy people
Mold infection is a separate problem. For healthy people, the risk from indoor mold is low. Fungal pneumonia mainly strikes people whose immune defenses are down, such as people with HIV, blood cancers or an organ transplant, or people taking steroids or other drugs that weaken those defenses.
Does mold cause inflammation in the whole body?
This is what most people want to know. The honest answer is that nobody knows yet.
Fungal proteases can break down the airway's barrier and set off alarm signals that drive allergic inflammation.From a 2026 review in Front Immunol
The best clue comes from Finland. Researchers inspected the homes of 291 children at age 6 and tested their blood. Children with major moisture damage in the living room, kitchen or their bedroom, or with damp and mold in the bathroom, had higher CRP (C-reactive protein, a blood marker of inflammation), and their blood made more inflammation signals when tested in the lab. White blood cell counts did not differ. Neither did FeNO, a breath test for airway inflammation. The authors wrote only that mold "may be associated" with low-level, body-wide inflammation.
That is one study at one point in time. It can't prove the mold was to blame.
The German medical guideline on indoor mold found too little evidence to link damp and mold with arthritis, COPD, sarcoidosis or cancer. What about mycotoxins, the chemicals some molds make? Only molds able to make them can poison anyone, and indoor air levels are always very low. So claims that mold inflames your whole body run well ahead of the research.
How doctors measure it
No single blood test measures "mold inflammation." Doctors look where the problem is.
For allergy, a 2024 review based on the updated German guideline says a sound work-up starts with your history and an exam. With signs of allergy, the next step is a skin prick test or a blood test for IgE, the antibodies behind allergies.
For airway inflammation in asthma, doctors can use FeNO: you breathe into a device that measures nitric oxide, and higher levels point to type 2 inflammation. In people with asthma, FeNO usually rises above 25 parts per billion. It also helps show whether a steroid inhaler is working.
For HP, doctors rely on a careful exposure history, a CT scan, IgG antibody tests against the suspected trigger, and often fluid washed from the lungs for testing.
What the 2024 review does not recommend: blood or urine tests for mold parts or mold chemicals, or measuring mold, mold gases or mycotoxins in your home as part of a medical work-up. The 2017 guideline adds that no validated mycotoxin tests exist for medical care.
What has been tested
We gathered every tested approach in our sources into one table. Notice what is missing: none of these studies measured blood markers like CRP. They measured symptoms and lung function.
| Approach | Study type | What was measured | Result |
|---|---|---|---|
| Repairing mold-damaged homes, adults | Two studies in a Cochrane review | Wheezing; runny, stuffy nose | Odds of wheezing about a third lower (OR 0.64); odds of a stuffy, runny nose lower (OR 0.57) |
| Repairing homes vs. information only, children | One study in a Cochrane review | Asthma days, emergency visits | No difference |
| Repairing mold-damaged schools | Studies in a Cochrane review | Pupils' symptoms, doctor visits | Symptoms mixed; fewer doctor visits for colds |
| Removing home mold, people with HP | Look-back cohort study, 2025 | Lung capacity (FVC) | 5 of 41 improved by more than 10% |
OR means odds ratio. Below 1 means lower odds.
The Cochrane review, a careful kind of review known for strict methods, pooled 12 studies with 8,028 people, and the repairs ranged from full renovation to cleaning only. Its adult findings were moderate-quality evidence.
The HP numbers deserve a second look. Five of 41 is about 1 in 8 people. That is a small share, and avoiding the trigger is still the main treatment for HP. But some people with scarred lungs from HP keep getting worse even after the exposure ends.
What helps
Tick what you'll try this week. Your picks stay on this device.
Put together, the path is clear. Mold's inflammation starts in the airway lining, and the biggest proven lever is getting the mold, and the water feeding it, out of your home.
you have asthma and it gets worse at home (keep taking your medicines as prescribed and ask before changing them); you have a weak immune system, for example from cancer treatment, an organ transplant or medicines that lower immunity; you get more short of breath over weeks or months; a child in your home has wheeze or repeated chest infections; or you are pregnant and planning to clean up mold yourself.
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How this article was made
Researched and written from 14 peer-reviewed papers. Our automated check matched every claim against the exact words of its source, confirmed every paper exists in PubMed, and found none retracted. Checked November 5, 2026. Not individually reviewed by a doctor. Photos are illustrative; the people in them are not patients or readers.
Grades run Strong, Moderate, Emerging, Early and Not supported, and the grade decides the words we may use. How we grade evidence · Medical disclaimer
Sources
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- ReviewImmunity to fungi in the lung.Heung LJ, Wiesner DL, Wang K et al. Semin Immunol, 2023.PubMedFull paper
- GuidelineMedical diagnostics for indoor mold exposure.Hurraß J, Heinzow B, Aurbach U et al. Int J Hyg Environ Health, 2017.PubMedFull paper
- ReviewIndoor Mold—Important Considerations for Medical Advice to Patients.Hurraß J, Nowak D, Heinzow B et al. Dtsch Arztebl Int, 2024.PubMedFull paper
- Cross-sectionalMoisture damage in home associates with systemic inflammation in children.Mustonen K, Karvonen AM, Kirjavainen P et al. Indoor Air, 2016.PubMedFull paper
- ReviewUnderstanding the Cellular Sources of the Fractional Exhaled Nitric Oxide (FeNO) and Its Role as a Biomarker of Type 2 Inflammation in Asthma.Escamilla-Gil JM, Fernandez-Nieto M, Acevedo N Biomed Res Int, 2022.PubMedFull paper
- ReviewRelationship between Aspergillus and asthma.Agarwal R, Muthu V, Sehgal IS Allergol Int, 2023.PubMedFull paper
- GuidelineDiagnosis of Hypersensitivity Pneumonitis in Adults. An Official ATS/JRS/ALAT Clinical Practice Guideline.Raghu G, Remy-Jardin M, Ryerson CJ et al. Am J Respir Crit Care Med, 2020.PubMedFull paper
- Meta-analysisRemediating buildings damaged by dampness and mould for preventing or reducing respiratory tract symptoms, infections and asthma.Sauni R, Verbeek JH, Uitti J et al. Cochrane Database Syst Rev, 2015.PubMedFull paper
- ReviewHypersensitivity pneumonitis.Costabel U, Miyazaki Y, Pardo A et al. Nat Rev Dis Primers, 2020.PubMedFull paper
- CohortHypersensitivity pneumonitis associated with home mold exposure: A retrospective cohort analysis.Adams TN, Redlich CA, Glazer CS et al. PLoS One, 2025.PubMedFull paper
- ReviewInnate and adaptive immune responses to fungi in the airway.Bartemes KR, Kita H J Allergy Clin Immunol, 2018.PubMedFull paper
- ReviewInnate airway immune response to fungal allergens.Binoy AC, Brack S, Doherty TA Front Immunol, 2026.PubMedFull paper
- ReviewRoles of Dectin-1 in Allergic Airway Inflammation.Hirose K, Ito T, Nakajima H Crit Rev Immunol, 2017.PubMedFull paper
