About Hypersensitivity Pneumonitis
Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is an immune-mediated inflammatory lung disease caused by repeated inhalation and deposition of organic or inorganic antigens in the lungs, triggering complex Type III and IV hypersensitivity reactions. Common antigens include bird proteins (avian serum antigens in bird fancier's lung), mold spores (farmer's lung, bagassosis from moldy sugarcane), metal salts (metal worker's lung, beryllium disease), thermophilic actinomycetes, and isocyanates.
Three clinical forms exist: acute (symptoms 4-6 hours after exposure with fever, chills, malaise resolving within days of avoidance), subacute (symptoms over days-weeks with continued exposure), and chronic (insidious development over months-years with progressive fibrosis). Pathophysiology involves immune complex deposition in lung tissue with lymphocytic infiltration, granuloma formation, and alveolitis.
Acute form presents with dyspnea, cough, fever, and malaise resolving within days of antigen avoidance. Chronic form progresses to irreversible pulmonary fibrosis. High-resolution CT shows centrilobular nodules, ground-glass opacities, and fibrotic changes. Diagnosis combines clinical history, exposure assessment, serology (precipitating antibodies), and imaging.
Common Symptoms of Hypersensitivity Pneumonitis
Recognizing the signs of Hypersensitivity Pneumonitis early can lead to faster diagnosis and better outcomes. Symptoms may vary in severity from person to person. If you or a loved one are experiencing any of the following, consider speaking with a specialist.
- Dyspnea and cough
- Fever and chills within hours of exposure
- Fatigue and malaise
- Weight loss in chronic form
- Progressive airflow obstruction
- Hypoxemia during exertion
Who Hypersensitivity Pneumonitis Affects
Can occur at any age but particularly affects adults in their 40s-60s with occupational or environmental exposures. Variable presentation between individuals based on antigen exposure intensity, duration, and host factors. Both males and females affected equally.
Genetic predisposition factors including HLA alleles being identified. More common in bird enthusiasts, farmers, agricultural workers, and those in occupational settings with repeated antigen exposure. Higher prevalence in developed nations with identified occupational exposures.
Find Your Next Step
FDA-Approved Treatments for Hypersensitivity Pneumonitis
There is currently 1 FDA-approved medication for Hypersensitivity Pneumonitis. These therapies represent the current standard of care and may be used alongside or compared against investigational treatments in active clinical trials.
Source: openFDA drug labeling data. This list may not include all treatments. Always consult your doctor.
Side Effect Explorer
Real-world side effect reports from the FDA Adverse Event Reporting System (FAERS). Includes both FDA-approved drugs and investigational therapies from active clinical trials. Click any drug to see what patients reported.
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Diagnosis and Testing
An immune reaction to inhaled antigens (mold, bird proteins, chemicals); diagnosis depends on exposure history, imaging, and sometimes inhalation challenge, not gene testing.
Trusted Hypersensitivity Pneumonitis Resources
Reputable organizations and medical references for learning more about Hypersensitivity Pneumonitis, including disease registries, foundation resources, and clinical guidelines.