Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Farmer’s lung is a type of hypersensitivity pneumonitis caused by inhaling organic dusts from moldy hay, straw, and grain. It leads to inflammation of the alveoli in the lungs due to an immune response.
Farmer's lung is primarily caused by repeated exposure to thermophilic actinomycetes found in moldy agricultural products.
It is classified as a Type III hypersensitivity reaction, involving immune complex deposition.
Symptoms include cough, shortness of breath, chills, and fever, typically appearing 4-8 hours after exposure.
Chronic exposure can lead to irreversible lung damage such as pulmonary fibrosis.
Diagnosis often involves a combination of clinical history, chest X-rays or CT scans showing interstitial changes, and positive precipitins in serum against antigens from moldy hay.
Related terms
Hypersensitivity Pneumonitis: An inflammatory syndrome affecting the lungs caused by inhalation of various environmental antigens.
Type III Hypersensitivity: An immune response involving antigen-antibody complexes that deposit in tissues and cause inflammation.