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Hypersensitivity Pneumonitis: Information on Causes, Diagnosis & Treatments

Inflammation Lung Harmful Chemicals Hypersensitivity pneumonitis is a serious condition caused by repeated exposure to one or more environmental substances through inhalation that leads to lung inflammation. This can include bacteria and Mycobacterium, mold, and fungi along with chemicals and proteins.

Many individuals who develop hypersensitivity pneumonitis are exposed to environmental sources that include:

  • Animal furs

  • Sawdust from hardwoods

  • Ventilation systems, humidifiers, and air-conditioners

  • Contaminated fluids used in metal processing

  • Bird feathers and droppings

  • Hot tubs

  • Animal feed products including grains and hay

  • Contaminated food industry products including corks and sausage casings

  • Contaminated foods including sugarcane, barley, grapes, and cheese

Decades ago, doctors believed that the different conditions associated with hypersensitivity pneumonitis represented a variety of separate lung diseases. However, medical science has determined that hypersensitivity pneumonitis is a single condition that is triggered by a variety of different substances. Without treatment, hypersensitivity pneumonitis can lead to chronic inflammation that irreversibly scars the lining of the lungs that could severely impair their capacity to function normally.

Who Is at Risk for Hypersensitivity Pneumonitis

Individuals most likely at risk of developing hypersensitivity pneumonitis have a compromised immune system that responds aggressively to specific substances. Usually, the body will respond to heavy exposure to an irritating condition within 4 to 12 hours.

The most common associated risks involving hypersensitivity pneumonitis include:

  • Age – Any individual at any age can develop hypersensitivity pneumonitis. However, on average, men and women between 50 and 55 years of age are the most susceptible to the condition.

  • Gender – While boys, girls, men, and women are all susceptible to developing hypersensitivity pneumonitis, women tend to be slightly more at risk of developing the condition.

  • Occupation or Environment – Repeated exposure to known antigens that can cause hypersensitivity pneumonitis can place any individual at risk of developing the condition. However, certain occupations including bird handlers, animal breeders, farmers, woodworkers, wine makers and those in the cheese industry have a higher risk due to exposure to substances the cause hypersensitivity pneumonitis.

  • Genetic Predisposition – Medical scientists believe that genetics plays a crucial role in some people developing hypersensitivity pneumonitis if repeatedly exposed to causative substances. In addition, a family history of the disease and/or pulmonary fibrosis might increase in individuals risk of developing the condition.

  • Lifestyle Habits – While smoking does not appear to be a direct cause of hypersensitivity pneumonitis, smoking tobacco products is thought to worsen many of the complications associated with the condition.

  • Other Medical Issues – Experiencing a viral infection when growing older can increase the potential risk of developing the condition. Some individuals who previously had hypersensitivity pneumonitis can experience a recurrence of the condition if they have certain other medical issues.

The lung can become compromised by the damage that occurs to certain white blood cells (lymphocytes) in the body. Initial exposure often causes the lymphocytes to sensitize and produce antibodies that will eventually cause tissue damage.

As the lungs become inflamed, lymphocytes continuously cause damage to repeated antigen exposure that can produce recurrent chronic inflammatory responses and manifests itself as a buildup of lymphocytes in the walls of the small airways and alveoli (tiny air sacs in the lungs). If the lymphocytes continue to build up it can cause serious progression of the disease and an exacerbation of symptoms.

Common Symptoms

Common symptoms associated with acute hypersensitivity pneumonitis involve:

  • General malaise

  • Chest tightness

  • Shortness of breath

  • Excessive coughing

  • Chills and fever

However, symptoms between individuals vary greatly based on the exposure, medical health history and type of antigen that causes the acute, subacute or chronic condition. Some individuals experienced irreversible lung damage, pulmonary hypertension, and/or heart failure that is a direct result of the signs and symptoms associated with hypersensitivity pneumonitis.

Diagnosing Hypersensitivity Pneumonitis

Doctors diagnose hypersensitivity pneumonitis in three distinct categories that include acute, subacute, and chronic. Only a limited number of individuals exposed to reactive substances will develop symptoms that could appear weeks or months later.

To accurately diagnose hypersensitivity pneumonitis, the doctor will usually order a variety of tests that include:

  • High-resolution CT (computerized tomography) scans

  • Chest x-ray

  • Bronchoalveolar lavage

  • Serologic tests that analyze blood serum

  • Pulmonary function tests

  • Histologic examinations where the structure of affected tissue is analyzed under a microscope

As a part of the diagnosis of hypersensitivity pneumonitis, the doctor will need to categorize the condition in one of three categories including acute, subacute, and chronic. Categorizing the disease will help determine the best method of treatment based on the patient's overall health, the length of exposure and the damage it has caused.

  • Acute Hypersensitivity Pneumonitis – This form of the pneumonitis develops in individuals who have been previously sensitized to a high-level antigen where the symptoms will manifest as a cough, chills, fever, or significant chest tightness like in asthmatic patients. Usually, labored or difficult breathing (dyspnea) will develop 4 to 8 hours after exposure. The patient might also display signs of vomiting, nausea, or anorexia upon physical examination or the doctor may detect inspiratory crackles or an absence of wheezing when listening to the chest cavity.

  • Subacute Hypersensitivity Pneumonitis – The subacute form of the disease presents some characteristics of both acute and chronic pneumonitis and can manifest with labored breathing, coughing, anorexia, or fatigue that can develop within a few days or up to two weeks after exposure to the substances.

  • Chronic Hypersensitivity Pneumonitis – The chronic condition usually involves individuals who have a low-level long-term exposure to antigens including bird owners. The condition will create complications like unexpected weight loss, fatigue, coughing, and exertional labored breathing. Chronic cases are usually absent of fevers, however, when the disease advances, the body can develop pulmonary fibrosis resulting in respiratory failure, right heart failure, or both.

Treating the Condition

Typically, the doctor will recommend a regimen of corticosteroids including prednisone that is taken for one to two weeks or longer. However, it is essential that the patient follows the doctor's orders at weaning away from prednisone medication that can cause serious side effects if the dosage is not decreased slightly in weekly decrements. Treating chronic hypersensitivity pneumonitis usually requires extensive courses of prednisone at higher dosages where tapering off the medication will be based on clinical response.

Without proper treatment, the disability associated with hypersensitivity pneumonitis can progress and become irreversible in time. Individuals who have suffered an acute episode of the condition typically recover completely if they continuously avoid the substance that initiated the body's reaction.


The easiest way to prevent acquiring hypersensitivity pneumonitis is to avoid exposure to known antigens that could involve environmental toxins, bird droppings, and contaminated food. When around dust, it is essential to follow control measures by dampening compost, wearing protective masks or using air filters. Treating the area with an effective fungicide can help prevent the growth of harmful antigenic microorganisms found in sugarcane and hay.

Ventilation systems should be extensively cleaned and moist and moldy carpets removed to minimize the level of humidity that can help exacerbate the growth of fungus and mold that could lead to hypersensitivity pneumonitis. However, even taking these measures might not provide complete protection against the damaging effects of antigens that directly cause the condition.

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