Overview
Alternaria is a genus of molds best known for one thing: allergy. Alternaria alternata, the main species studied in allergy research, is mainly an outdoor fungus. Its spores spread in warm, dry air and, in temperate climates, peak in summer. It can also be found in damp, poorly ventilated homes.[1]
Alternaria is a major aeroallergen in many parts of the world. Sensitivity to it has been increasingly recognized as a risk factor for the development and persistence of asthma, for asthma severity, and for potentially fatal asthma attacks.[2] It has also been implicated in thunderstorm asthma.[3]
Classification
- Phylum: Ascomycota
- Family: Pleosporaceae
- Genus: Alternaria
- Best-known species: A. alternata
Mold allergy has a long history. Mold-induced respiratory allergy was first described in 1698, but Alternaria was only linked to it in 1930, when its spores were found to cause allergic asthma.[1] Researchers have since isolated 16 allergens from A. alternata, many of them enzymes.[1]
Health Significance
Allergy and asthma severity
A review of the evidence found a close association between fungal sensitization and asthma severity, involving several airborne fungi including Alternaria. Whether this relationship is causal is not yet confirmed.[4] Clinicians have described a patient with Alternaria allergy who developed an acute, life-threatening asthma attack during peak Alternaria season.[2]
Thunderstorm asthma
On July 29, 2002, a thunderstorm in the United Kingdom was followed by an epidemic of asthma admissions. A case-control study of 26 patients treated at Cambridge University Hospital found:[3]
| Finding | Result |
|---|---|
| Patients sensitized to Alternaria | 23 of 26 |
| Odds of storm-related asthma if sensitized to Alternaria | 9.31 times higher (95% CI 2.31–37.60) |
| Airborne spores during the storm | Increased Alternaria, Cladosporium, and Didymella |
The authors concluded that Alternaria sensitivity is a compelling predictor of epidemic asthma in people with seasonal asthma and grass pollen allergy, and is likely an important factor in thunderstorm asthma.[3] The study was small, which is why the confidence interval is wide.
Indoor exposure
Although it is mainly an outdoor mold, Alternaria also matters indoors. A nationally representative U.S. survey of 831 homes and 2,456 people measured Alternaria antigens in household dust. Compared with the lowest third of exposure, people in homes with the highest third of Alternaria antigen levels had 84% higher adjusted odds of asthma symptoms in the past year (odds ratio 1.84, 95% CI 1.18–2.85).[5] As a cross-sectional study, it shows an association rather than proof of cause, but the authors suggested that reducing indoor Alternaria exposure may help control asthma.[5]
Diagnosis
Alternaria allergy is diagnosed with skin prick testing or blood tests for specific IgE, interpreted alongside symptoms. Commercial Alternaria extracts used for testing and immunotherapy vary and are not fully standardized, because they are often mixtures of allergenic ingredients and impurities. Purified allergen molecules may improve this in the future.[1]
Reducing Exposure
- Check mold spore counts during peak season and limit prolonged outdoor activity on high-count days if you are sensitized.
- Stay indoors with windows closed during thunderstorms if you have asthma and a mold or grass pollen allergy.
- Control indoor moisture with ventilation, dehumidification where needed, and prompt repair of leaks.
- Keep asthma well controlled and carry reliever medication as directed. Our allergies and hay fever protocol summarizes research on the microbiome's role in allergic disease.
Other common molds that affect allergy and asthma include Cladosporium, Penicillium, and Aspergillus. For mold in water-damaged buildings, see our guide to warning signs of mold toxicity.
When to See a Clinician
Seek urgent care for severe shortness of breath, difficulty speaking, blue lips, or a reliever inhaler that is not helping. See a clinician if asthma or allergy symptoms worsen in summer or after storms, if you need your reliever more often, or if you suspect mold at home is affecting your breathing.
This page is for educational purposes and is not medical advice. Consult a qualified healthcare provider about allergy testing, asthma management, and mold exposure.