Popcorn Lung: Causes and Symptoms

Introduction

Popcorn lung, formally known as bronchiolitis obliterans, is a rare and serious respiratory condition that affects the bronchioles of your lungs. “Bronchiolitis” refers to inflammation of the bronchioles, whereas “obliterans” means permanent narrowing of the bronchioles.

The bronchioles are the small airways in the lungs that branch off from the larger bronchi which enter each lung (Figure 1). In this condition, these bronchioles become inflamed, damaged, and then permanently scarred and narrowed. Bronchiolitis obliterans is caused by inhalation of toxic substances and chemicals.

It can also develop due to certain respiratory infections and medical conditions.¹ This condition can be life-threatening and, although there is no cure, early treatment can help to slow down the progression of the disease. Therefore, understanding the causes and symptoms of popcorn lung is crucial for its prevention and early detection.

What causes popcorn lung?

Popcorn lung is caused when the bronchioles of the lungs become damaged over time, leading to a cascade of respiratory problems. Several factors can contribute to this condition, including:¹

• Inhalation of harmful chemicals
• Lung infection
• Autoimmune diseases
• Organ transplants

Other medical conditions have also been associated with popcorn lungs, such as human immunodeficiency virus (HIV) and human herpes virus (HHV), as well as rare conditions like Castleman disease and paraneoplastic pemphigus.

When exposed to these triggers, the body’s immune system (your natural defence system) initiates an inflammatory response in your airways to try to fight off the perceived threat. While the bronchioles are typically capable of healing from this inflammation and injury, in some cases, this healing process can cause scarring of the bronchioles.¹

Over time, this scar tissue can build up within the bronchioles, causing narrowing and obstruction of these small airways. This interrupts airflow through the lungs, making breathing more challenging and preventing the complete expulsion of air when breathing out - known as “air-trapping”. Unfortunately, this scarring is irreversible and the disease will worsen over time as more scar tissue is formed. This can eventually result in respiratory failure, posing a serious threat to life.²

Chemical exposure

The risk of developing popcorn lung is increased in certain individuals due to exposure to toxic substances and chemicals that irritate the lungs and cause damage.

Bronchiolitis obliterans is called ‘popcorn lung’ because this disease was first identified in individuals who worked in a microwave popcorn factory. This condition was caused by inhalation of a chemical called diacetyl, which is used in factories to give popcorn a buttery taste.³

This chemical is also used as a flavouring agent in many other products, such as:

• Microwave popcorn
• Baked goods
• Sweets and chocolate
• Caramel and butterscotch
• Flavoured coffee

The use of diacetyl in e-cigarette liquids was banned in the UK in 2016 so e-cigarettes sold in the UK should not contain this chemical. As such, the NHS has stated that “vaping does not cause popcorn lung”. However, e-cigarettes imported from countries outside of Europe may contain this harmful chemical.^4,5

Other chemicals that may cause popcorn lung when inhaled include:¹

• Acetaldehyde - found in cannabis smoke and some e-cigarettes
• Ammonia
• Chlorine
• Formaldehyde - a chemical used in some glues and building materials
• Fumes from metal oxides - a common byproduct of welding
• Hydrochloric acid
• Nitrogen oxides
• Sulphur dioxide -  a pollutant released by burning fossil fuels
• Sulphur mustard -  a chemical warfare agent known as “mustard gas”

Medical conditions

Certain medical conditions can increase the risk of developing popcorn lung. These can include:^1,6,7,8

• Respiratory infections (e.g., respiratory syncytial virus (RSV), some forms of pneumonia and bronchitis)
• Viral infections (e.g., adenovirus, measles, flu)
• Autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus (SLE), inflammatory bowel disease)
• Stevens-Johnson syndrome - a rare drug-induced disorder of the skin and mucous membranes that develops as a severe reaction to some medication 

Inflammation and scarring from a lung transplant can also cause popcorn lung; this is thought to be a sign of organ rejection. In fact, popcorn lung is one of the most common non-infectious complications after a lung transplant, with over 50% of patients who have received a lung transplant reported to develop some degree of bronchiolitis obliterans within 5 years after the transplant.^1,9,10

Other transplant patients can also be at an increased risk of developing popcorn lung after a transplant. For example, up to 10% of haematopoietic stem cell transplantation (HSCT) patients develop popcorn lung within 5 years after the transplant.^11,12 When bronchiolitis obliterans develops after a transplant, it is generally called bronchiolitis obliterans syndrome (BOS).¹³

What are the symptoms of popcorn lung?

If you have had an illness or have been exposed to harmful chemicals, you might not develop symptoms of popcorn lung immediately. Instead, it can take between 2-8 weeks for the symptoms of popcorn lung to develop and become noticeable. The most common signs and symptoms of popcorn lung include:¹

• Chronic dry cough
• Shortness of breath (dyspnoea)
• Wheezing (a whistling sound when you breathe)

These symptoms typically flare up during or after exercise or exertion and generally worsen over time as the scarring builds up in your airways.

Other symptoms that some people with popcorn lung might experience include:

• Tiredness and fatigue
• Fever (high temperature)
• Unexplained weight loss
• Skin rash

It should be noted that many of these symptoms are similar to those of chronic obstructive pulmonary disease (COPD). It is important to see your healthcare provider if you have these symptoms. They will be able to conduct tests to determine the functioning of your lung and make an informed diagnosis.

Treatment of popcorn lung

As mentioned before, early diagnosis and treatment are vital to prevent progression and irreversible damage. Treatment involves slowing down the disease and treating symptoms. If the damage is due to inhalation of an environmental chemical, it is essential to remove this substance.

Popcorn lung treatment may include:

• Corticosteroids: (e.g., prednisone) work by suppressing the immune response and reducing inflammation
• Inhaled medication: (e.g., albuterol) assists with relieving wheezing, shortness of breath, and tight chestedness by causing bronchodilation of the bronchioles
• Steroids: prescribed in severe cases to fight inflammation. These drugs are effective but can have other side effects
• Nasal prong oxygen or oxygen face mask can be prescribed if oxygen saturation levels are low
• A lung transplant is rarely recommended but can also be a last-resort option

FAQs

How common is popcorn lung?

The exact prevalence of popcorn lung is not known, but it is thought to be an extremely rare lung disease in the general population. The stringent regulations and controls over the use of hazardous chemicals in industrial settings have significantly decreased the prevalence of popcorn lung in industrial workers. Instead, the most common way of getting popcorn lung now is after receiving a lung transplant.

Is popcorn lung contagious?

No, popcorn lung is not contagious. You cannot catch this disease from other people or pass it on to other people if you are infected.

What does the beginning of popcorn lung feel like?

The main symptoms of popcorn lung are a dry cough and shortness of breath which are most prominent during or after exercise. You might also notice a squeaking or wheezing sound coming from your chest or throat during normal breathing.

Does vaping cause popcorn lung?

There is currently no evidence that vaping can cause popcorn lung and there have been no confirmed cases of popcorn lung reported in people who use e-cigarettes in the UK. However, the effect that e-cigarettes have on the lungs is not yet fully understood and individuals considering vaping should be aware of its potential risks.

How long does it take to develop popcorn lung after exposure to a causative factor?

Symptoms typically take between 2-8 weeks to develop after you have inhaled a harmful chemical and gradually get worse over time. However, after a lung or stem cell transplant, symptoms may take longer to develop (typically 1-2 years). 

What is the difference between the symptoms of popcorn lung and asthma? 

The symptoms seen in popcorn lung are similar to those that occur in asthma, including a cough, shortness of breath, and wheezing. These symptoms are especially prominent during or after exercise. However, the symptoms in popcorn lung are persistent and develop over weeks to months, they are not episodic like asthma symptoms.

What is the difference between popcorn lung and bronchiolitis obliterans organising pneumonia?

Bronchiolitis obliterans organising pneumonia (BOOP) is a completely different disease to bronchiolitis obliterans (or popcorn lung), despite the similarity in the names. Both conditions do affect the lungs, specifically the bronchioles, however, BOOP is typically caused by an inflammatory disease or cancer and can be successfully treated – unlike popcorn lung. BOOP is now commonly referred to as cryptogenic organising pneumonia (COP).

Summary

Popcorn lung, or bronchiolitis obliterans, is a rare and serious lung condition caused by exposure to chemical vapours, such as diacetyl or by certain medical conditions, such as after a respiratory infection or after a lung transplant. Symptoms of popcorn lung typically develop between 2-8 weeks after exposure to these risk factors and include a chronic, dry cough, breathlessness, and wheezing during breathing.

These symptoms get worse over time as scar tissue builds up in the bronchioles which can result in respiratory failure – a potentially fatal condition. Therefore, recognising the underlying causes and symptoms of popcorn lung is essential for early diagnosis and effective intervention.