What Is Farmer's Lung?

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Farmers lung is part of a group of respiratory diseases known as interstitial lung disease. It is also a type of hypersensitivity pneumonitis - where the lungs are irritated by an environmental allergen (usually bacteria or fungus).

In the case of Farmer’s lung, the  allergens are usually bacteria or mould spores found in hay/crop dust. True to its name, it commonly affects farmers and other industrial workers that handle hay.

Symptoms usually begin after exposure and can disappear after you stop coming into contact with the allergen. However, repeated exposure to bacteria and mould spores can be particularly hazardous and cause lasting damage to your respiratory system. Symptoms range from a cough and difficulty taking a full breath to extreme cases of respiratory failure.

It is important to get diagnosed and treated for Farmer's lung to avoid complications. It is also essential to reduce or stop your exposure to bacteria and mould spores to prevent further damage.1

Causes of farmer's lung

Farmer’s lung may present after you’ve been exposed to bacteria or mould spores found in hay or crop dust often present on farms. Farmers and other industrial workers who work in close contact with crop dust daily will be prone to breathing in bacteria and mould which causes irritation to the lungs. This is because the body initiates an inflammatory immune reaction against these agents.1 

Other types of hypersensitivity pneumonitis can also affect the lungs in a  similar way to but due to different environmental allergens such as:

  • Flour
  • Sawdust 
  • Soil
  • Bird feathers/droppings
  • Animal fur
  • Water vapour (from humidifiers and hot tubs)
  • Lakes2 

Signs and symptoms of farmer's lung

Signs of farmer’s lung can onset quickly or slowly, sometimes noticeably and other times without obvious clinical presentation. Common symptoms include:

  • Difficulty taking deep breaths
  • Dry, chronic cough 
  • Lethargy 
  • Extreme tiredness 
  • Not feeling hungry 
  • Chills 
  • Fever3 
  • Muscle and joint pain1 

Bacteria and mould inhaled into the lungs can also cause the formation of:

  • Pulmonary fibrosis - thickening of lung tissue 
  • Granulomas - small mass of inflamed lung tissue1

Management and treatment for farmer's lung

The main way to manage a case of farmer's lung is to remove yourself from the environment where you  are being exposed to mouldy hay and crop dust. This may not be feasible for everyone due to professional constraints but it is still advisable to limit your exposure to the mould, for example, by using a “powdered dust respirator helmet” to avoid inhaling allergens.

Respiratory function can also be supported with:

  • Steroid treatment for short-term symptom relief 
  • Non-invasive ventilation to support breathing
  • Oxygen delivery to supply the vital organs 
  • Vaccinations to protect against infectious agents 

Lung transplants are usually performed as a last resort in severe cases with a poor prognosis.1 

Diagnosis of farmer's lung

Farmer’s lung can be hard to diagnose as signs of the disease are similar to other common respiratory infections like the cold,flu, chronic pulmonary obstructive disease (COPD) and the side effects of long term smoking.

Diagnosis primarily relies on clinicians asking about any possible exposure to mouldy hay, when and what symptoms appear, and how long you’ve been suffering from them. 

Diagnostic tests which may utilised include: 

  • Blood sampling (to analyse your white blood cell count - a higher than normal count may indicate Farmer’s lung)
  • Spirometry test (using a device to measure air volume in the lungs when breathing)
  • CT scanning (to look for physical abnormalities in the lung structures)
  • Bronchoscopy (a procedure where a tiny camera is inserted down the bronchi to closely examine the lung tissue) 
  • Lung biopsy (removing a tiny piece of lung tissue to be analysed in a hospital lab)1


Severe cases of farmer’s lung may require hospitalisation in order for patients to receive respiratory support if their condition progresses to respiratory failure and shock (low blood oxygen and lack of organ oxygenation). Severe cases can lead to eventual death if no treatment is given.1 


How can I prevent Farmer's lung?

Farmer’s lung can usually be prevented by limiting your exposure to allergic antigens (hay and dust mould spores). However, this may be unavoidable in some cases (if you live on a farm or work closely with these allergens in your profession). 

If this is the case, you should wear a personal protective “powdered dust respirator mask” when working to avoid inhalation of allergens. Wearing Personal Protective Equipment(PPE) may reduce symptoms but not completely prevent farmer’s lung.1 

How common is Farmer's lung?

Estimating the prevalence of farmer’s lung is difficult as the disease is often misdiagnosed when doctors assess the condition, or not may not diagnosed at all if patients do not seek treatment.1 

Who is at risk of Farmer's lung?

The group most at risk is usually farmers and other farm workers as they are regularly exposed to contaminated hay and dust. However, the disease is not completely exclusive to the agricultural profession as others who regularly handle spoiled hay may also be at risk of farmer’s lung.1 

When should I see a doctor?

You should see your doctor if you are struggling with otherwise unexplained respiratory symptoms. You should also see your doctor to rule out any other respiratory infections or conditions.1 


Farmer’s lung is a respiratory infection that commonly affects farmers, agricultural and other industrial workers. When mouldy and bacteria-ridden hay or crop dust enter the respiratory system, it can progressively make it hard to breathe properly and supply the body with enough oxygen to function. Sufferers will also feel generally unwell and lethargic. 

Farmer’s lung can be prevented by avoiding hay and crop dust exposure and there are also some available treatments that can help to alleviate symptoms. Some cases of Farmer’s lung have a poor prognosis when damage to the lungs is severe, so it is important to get diagnosed and treated as soon as possible. 

If you are concerned about your respiratory health or suspect you may have Farmer’s lung, don’t hesitate to contact your doctor to get checked. 


  1. Zergham AS, Heller D. Farmers lung. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 June 3]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK557580/ 
  2. Riario Sforza GG, Marinou A. Hypersensitivity pneumonitis: a complex lung disease. Clin Mol Allergy [Internet]. 2017 Mar 7 [cited 2023 Jun 3];15:6. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5339989/ 
  3. Leone PM, Richeldi L. Current diagnosis and management of hypersensitivity pneumonitis. Tuberc Respir Dis (Seoul) [Internet]. 2020 Apr [cited 2023 Jun 3];83(2):122–31. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7105432/

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Amy Murtagh

BSc Veterinary Bioscience - Bachelors of Science, University of Glasgow

Amy is a recent graduate from Glasgow's School of Biodiversity, One Health and Veterinary Medicine with a particular interest in science communication in these subject areas.

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