What Is Hypersensitivity Pneumonitis?
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Hypersensitivity Pneumonitis - Causes, Symptoms, Diagnosis, and Treatment

Published on Jul 27, 2022 and last reviewed on Nov 29, 2022   -  4 min read


Hypersensitivity pneumonitis causes an inflammatory lung. Read the article to learn about the symptoms, diagnosis, and treatment of hypersensitivity pneumonitis.

Hypersensitivity Pneumonitis - Causes, Symptoms, Diagnosis, and Treatment


Hypersensitivity pneumonitis is defined as an inflammatory lung condition due to allergic reactions. When foreign agents like mold or bacteria reach the tiny air sacs (alveoli) in the lungs through the airways (bronchi), it irritates the alveoli and causes sensitive reactions. The flexibility of the air sacs is lost, and it becomes rigid. The gaseous exchange becomes difficult. The hypersensitivity pneumonitis is curable if symptoms are treated earlier.

What Are the Causes of Hypersensitivity Pneumonitis?

The immune system produces inflammatory substances in response to allergic reactions. There is an increased number of white blood cells in the bloodstream. There is a collection of fluid in the alveoli (air sacs) due to the inflammation. The oxygen exchange occurs in tiny air sacs. But the fluid interrupts the air exchange between the alveoli and blood. The foreign agents that cause hypersensitivity pneumonitis are as follows;

  • Microbes - Microbial organisms like bacteria and fungi or mold irritates the air passages.

  • Chemicals - Harmful chemicals that trigger allergic reactions damage the air sacs (alveoli).

  • Animals and Birds - The fur of animals, the feathers, and the excreta of birds enter the respiratory tract and cause sensitive reactions.

  • Contaminated Food - Hypersensitivity pneumonitis occurs due to the presence of mold in contaminated food like cheese, bread, and barley.

  • Occupational Exposure - The workers involved in wood carving inhale wood dust. This causes allergic reactions in the airways.

  • Home Appliances - Hot tubs, air coolers, and humidifiers also cause hypersensitivity pneumonitis due to the growth of molds. This condition is also known as the humidifier lung.

  • Drugs - Medications like antibiotics, drugs used in chemotherapy for cancer, and cardiac failure have potential side effects like pneumonitis.

  • Radiation Therapy - Radiation therapy is given to patients during bone marrow transplants or to treat lung tumors affected by hypersensitivity pneumonitis later due to high-frequency radiation exposure.

  • Farmers - The mold present in the grains and hay is inhaled by the farmers during harvest. Pesticides are used to prevent insects. The aerosol mist reaches the air sacs through the nasal openings. It results in hypersensitivity pneumonitis.

Symptoms of hypersensitivity pneumonitis

What Are the Symptoms Associated With Hypersensitivity Pneumonitis?

The initial symptoms appear six hours after the entry of irritants into the air sacs. The symptoms of hypersensitivity pneumonitis are similar to the normal flu. If the symptoms do not subside in a few days, then consider it chronic pneumonitis. It is a long-term condition. The symptoms are as follows;

  • Fever - There is a high temperature due to foreign body reactions.

  • Chills - The respiratory illness due to the inflammation causes chills.

  • Myalgia and Arthralgia - The weak immune system affects the joints and muscles. The patient has pain in the muscles and joints.

  • Headache - Frequent headache is present in hypersensitivity pneumonitis.

  • Cough - The irritation in the upper respiratory tract causes a dry cough with slight discomfort.

  • Chest Pain - In severe hypersensitivity pneumonitis, both the lungs are involved. It results in chest pain.

  • Weight Loss - The patient feels tired and loses weight due to the loss of appetite.

How Is Hypersensitivity Pneumonitis Diagnosed?

The hypersensitivity pneumonitis condition is reversible if the person stays away from the triggering agent. The medical professionals take a few diagnostic tests to confirm the hypersensitivity pneumonitis. They are as follows;

  • Blood Test - The blood test is useful to distinguish hypersensitivity pneumonitis from other respiratory illnesses. The number of eosinophils increases in the blood due to allergic reactions in the lungs.

  • Chest X-Rays - This test is painless and covers the areas in the chest. The radiographic image captures both the lungs to identify any abnormality.

  • Computerized Tomography (CT) Scan - The time taken to scan the chest is around 15 minutes. The inflammation causes changes in the lung tissue. This can be assessed using computed tomography. It gives a comprehensive image of the lungs, airways, and air sacs.

  • Pulmonary Function Test - The amount of air exchanged during inspiration and expiration is measured with the help of a special diagnostic device called a spirometer. For this, the patient must fill the lungs during inspiration. The time taken by the person to expire the carbon dioxide is measured using a spirometer. The results are useful for identifying the working capacity of the lungs.

  • Bronchoscopy - The surgeon inserts the flexible tube into the oral cavity to reach the air sacs. The fluid present in the air sacs is collected as a sample for lab examination. A saltwater solution is used to remove the cells from the lungs. This surgical procedure is also known as lavage.

  • Biopsy - Major tissue cannot be removed using bronchoscopy. In that case, surgical removal of the lung tissue is performed. This procedure is known as a biopsy. The sample is used to observe respiratory ailments.

What Are the Treatment Methods for Hypersensitivity Pneumonitis?

  • Corticosteroids - Steroids are used to reduce the inflammatory changes in the lungs and airways. The most commonly used corticosteroid to treat hypersensitivity pneumonitis is Prednisone.

  • Oxygen Therapy - If the patient has shortness of breath due to pneumonitis, artificial oxygen support or hyperbaric oxygen therapy can be given to ease the breathing. The oxygen can be delivered through the mask.

  • Bronchodilators - The hypersensitivity reaction in the airways causes inflammation and narrowing of the bronchi (airways). This results in breathing difficulty. Bronchodilators are prescribed to dilate the air passages for easier air exchange in the lungs.

  • Surgery - If there is severe damage to the lungs due to hypersensitivity pneumonitis, the patient experiences respiratory failure. In that case, the patient needs lung transplant surgery to facilitate the respiratory mechanism.


Severe hypersensitivity pneumonitis causes scarring in the lung tissue. This damages the lungs and is a permanent condition. The scarring makes the lung stiff and slows down respiration. Untreated hypersensitivity pneumonitis leads to pulmonary fibrosis in the future. Many people recover with mild symptoms. Long-term hypersensitivity pneumonitis is a very rare condition. It often occurs in elderly people above the age of 50 years. Avoid working in a field filled with dust particles.

Last reviewed at:
29 Nov 2022  -  4 min read




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