How fungal spores interact with asthma and other lung diseases
Every day we inhale thousands of microscopic fungal spores from the environment. One of the most common fungi in the air is Aspergillus fumigatus. In healthy lungs these spores are removed quickly by the lungs’ natural defence systems and cause no illness.
However, in people with asthma—particularly severe asthma—the interaction between the lungs and Aspergillus can be very different. The fungus may trigger allergic inflammation, grow in mucus within the airways, or occasionally contribute to chronic lung disease.
Understanding this relationship helps explain several important conditions including:
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Aspergillus sensitisation
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Severe Asthma with Fungal Sensitisation (SAFS)
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Allergic Bronchopulmonary Aspergillosis (ABPA)
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Aspergillus bronchitis
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Chronic Pulmonary Aspergillosis (CPA)
Although asthma is the most common condition linked to Aspergillus allergy, other lung diseases such as bronchiectasis, Chronic Obstructive Pulmonary Disease (COPD), and tuberculosis-related lung damage can also create environments where the fungus becomes important.
Why Asthma Creates a Favourable Environment for Aspergillus
Asthma is a disease of airway inflammation and hyper-reactivity. The bronchi narrow during attacks because the airway wall becomes swollen and the surrounding smooth muscle contracts.
Several features of asthma make it easier for Aspergillus spores to remain in the lungs.
Mucus production
Asthma often causes increased production of thick airway mucus.
Normally mucus traps inhaled particles and moves them upward toward the throat via the mucociliary escalator.
In asthma:
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mucus becomes thicker
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clearance becomes less efficient
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spores remain trapped
This trapped environment allows fungal spores to persist in the airway mucus.
Allergic immune responses
Many asthma patients have Type-2 (T2) inflammation (50-70%), involving immune pathways driven by:
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Immunoglobulin E (IgE)
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Interleukin-4
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Interleukin-5
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Interleukin-13
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eosinophils
These pathways respond strongly to fungal allergens. When the immune system recognises Aspergillus proteins it may trigger allergic inflammation in the airways.
Fungal sensitisation is increasingly recognised as an important contributor to severe asthma (PMID: 24735832).
Aspergillus Sensitisation
Many people with asthma develop allergic sensitisation to Aspergillus.
Sensitisation means the immune system produces antibodies against fungal proteins.
Features include:
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positive Aspergillus skin test or IgE blood test
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worsening asthma symptoms
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increased exacerbations
Studies suggest 10–25% of patients attending severe asthma clinics show Aspergillus sensitisation (PMID: 24735832).
However, sensitisation alone does not necessarily cause lung damage.
Severe Asthma with Fungal Sensitisation (SAFS)
Some patients with severe asthma have fungal sensitisation but do not meet the criteria for ABPA.
This condition is known as Severe Asthma with Fungal Sensitisation (SAFS).
Typical features include:
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severe or poorly controlled asthma
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fungal allergy
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moderate IgE elevation
A randomised controlled trial demonstrated that antifungal therapy may improve symptoms in some SAFS patients (PMID: 18948425).
Allergic Bronchopulmonary Aspergillosis (ABPA)
Allergic Bronchopulmonary Aspergillosis is the most important Aspergillus-related disease associated with asthma.
ABPA occurs when Aspergillus grows within airway mucus and triggers a strong allergic immune response.
Typical findings include:
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very high total IgE levels
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Aspergillus-specific IgE and IgG antibodies
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eosinophilia
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mucus plugs containing fungal hyphae
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central bronchiectasis
ABPA occurs in approximately:
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1–2% of all asthma patients
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up to 10–15% of severe asthma patients
These figures come from global prevalence estimates of ABPA in asthma populations (PMID: 23210682/.
Modern diagnostic criteria for ABPA were updated by the International Society for Human and Animal Mycology (ISHAM) in 2024 (PMID: 38423624).
Asthma and Aspergillus Disease Pathway
Possible interactions between asthma and Aspergillus. Some patients develop allergic disease (ABPA) which may lead to airway damage such as bronchiectasis (NB Progression to CPA is very rare).
When ABPA Causes Bronchiectasis
Repeated inflammation from ABPA may damage airway walls and lead to bronchiectasis.
Bronchiectasis occurs when airways become:
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permanently widened
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distorted
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unable to clear mucus effectively
Instead of being cleared from the lungs, mucus pools in the airways.
This retained mucus creates an environment where microorganisms—including fungi—can grow.
Aspergillus Bronchitis
In some patients with bronchiectasis or chronic lung disease, Aspergillus may persist in airway mucus and cause chronic airway infection rather than allergy.
Symptoms may include:
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chronic cough
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sputum production
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repeated positive Aspergillus cultures
IgE levels are usually lower than in ABPA.
Chronic Pulmonary Aspergillosis (CPA)
Chronic Pulmonary Aspergillosis is a slowly progressive fungal infection of damaged lung tissue.
CPA usually develops in lungs containing:
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cavities
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severe structural damage
Common underlying diseases include:
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tuberculosis
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sarcoidosis
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severe COPD
Globally, the most common cause of CPA is previous tuberculosis infection (PMID: 22271943).
Asthma alone rarely causes CPA, but severe bronchiectasis or ABPA-related lung damage may occasionally lead to it.
Aspergillosis and Immune Competence
Different forms of aspergillosis occur depending on lung damage and immune function.
Other Lung Diseases Linked to Aspergillus
Although asthma is the most common condition associated with Aspergillus allergy, several other lung diseases can predispose to fungal disease.
Bronchiectasis
Dilated airways trap mucus, allowing fungi and bacteria to persist.
COPD
Chronic airway inflammation may lead to Aspergillus bronchitis or chronic pulmonary aspergillosis.
Tuberculosis
Post-tuberculosis lung cavities are the most common global cause of chronic pulmonary aspergillosis (PMID: 22271943).
Key Messages
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Asthma is one of the most important diseases associated with Aspergillus-related lung conditions.
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Many asthma patients develop fungal sensitisation.
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A smaller proportion develop Allergic Bronchopulmonary Aspergillosis (ABPA).
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Repeated inflammation from ABPA can lead to bronchiectasis.
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Chronic pulmonary aspergillosis is rare in asthma alone but may occur if significant lung damage develops.
Understanding these interactions helps guide diagnosis and treatment for people living with asthma and Aspergillus-related disease.
Further reading
Agarwal R, Chakrabarti A, Shah A, Gupta D, Meis JF, Guleria R, Moss R, Denning DW; ABPA complicating asthma ISHAM working group. Allergic bronchopulmonary aspergillosis: review of literature and proposal of new diagnostic and classification criteria. Clin Exp Allergy. 2013 Aug;43(8):850-73. doi: 10.1111/cea.12141. PMID: 23889240.
Denning DW, Pleuvry A, Cole DC. Global burden of chronic pulmonary aspergillosis as a sequel to pulmonary tuberculosis. Bull World Health Organ. 2011 Dec 1;89(12):864-72. doi: 10.2471/BLT.11.089441. Epub 2011 Sep 27. PMID: 22271943; PMCID: PMC3260898.
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