Causes of bronchitis

What causes bronchitis? Common acute and chronic causes of bronchitis

Immune System Expert
Ask Dr. Jen Tan

An introduction to causes of bronchitis

Bronchitis can be acute (short-term) or chronic (long-term) and occurs when an irritant or infection causes inflammation and swelling to the lining of the bronchial tubes (the tubes that carry air to and from your lungs).

When these tubes get infected, they swell, and start to produce mucus, which makes breathing more difficult. This causes a cough to develop, as the body attempts to expel the irritant/infection and the excess mucus from the air passages and lungs.

What causes bronchitis?

Acute bronchitis is most often caused by viruses - typically the same viruses that cause the common cold, flu and other respiratory infections, whereas the most common cause of chronic bronchitis is smoking.

Bacterial infections, although less common, can also trigger bouts of acute bronchitis, as well as worsen chronic bronchitis.

Respiratory irritants such as air pollution, dust and chemical fumes can sometimes cause both acute and chronic bronchitis, but it is most commonly associated with chronic bronchitis.

Viral infections & bronchitis

Up to 95% of acute bronchitis cases is caused by a viral infection (the same viruses that cause the common cold and flu).1 The most common viruses are rhinovirus, adenovirus, influenza A and B, and parainfluenza virus.

These viruses spread through the air when people cough, through physical contact or by touching infected surfaces.

When the body tries to fight the infection, it causes the bronchial tubes to swell and become inflamed. This inflammation is the body’s natural response to infections to aid healing. However, as the bronchial tubes swell and thicken, the airways become narrowed, constricted and can become blocked with excess mucus, restricting airflow to the lungs and causing the symptoms of bronchitis.

A persistant cough is the most common symptom of acute bronchitis and develops as the body attempts to remove the infection or excess mucus from the air passages of the lungs.

In some instances, although less common, acute bronchitis can also be caused by a bacterial infection.

Repeated attacks of acute bronchitis caused by viral or bacterial infection can increase your risk of developing chronic bronchitis.

Those who already have chronic bronchitis are also often more susceptible to developing viral and bacterial infections, which can worsen chronic bronchitis symptoms.

Smoking & bronchitis

People who smoke or who live with a smoker have a higher risk of developing both acute bronchitis and chronic bronchitis.2 Smoking is the most common cause of chronic bronchitis, which is sometimes called a ’smoker's cough’.

When smoke is inhaled into the lungs, it contains thousands of harmful chemicals which irritate the lining of the bronchial tubes, causing them to thicken and become inflamed.

Persistent, long-term inflammation caused by smoking can cause serious damage to the bronchial tubes, making them narrower. This on-going irritation and inflammation can also cause the mucous membranes of the bronchial tubes to produce more mucus than usual, clogging up the bronchial tubes, restricting airflow and causing a persistent productive (mucus-producing) cough to develop.

Smoking also negatively impacts your immune response, making you more susceptible to viral and bacterial infections; this can increase your risk of developing acute bronchitis and slow down your recovery if you have acute bronchitis.

Occupational bronchitis

Occupational bronchitis, also known as industrial bronchitis, can affect people who, due to their work, are continually exposed to material in the air that can irritate and cause damage to the lungs, such as dust, fumes, chemicals, smoke and other harmful substances.

Jobs that may have a higher risk of workers developing bronchitis include coal mining, welding, asbestos work, grain handling and those who work with textiles (fabrics).

Occupational bronchitis usually eases once you are no longer exposed to the irritant or have taken steps to reduce your exposure; however, prolonged exposure on an ongoing basis can seriously damage your airways, which increases the risk of developing chronic bronchitis.

If you work in an environment where you are heavily exposed to irritants, speak to your supervisor or HR manager about respiratory protective equipment such as masks.

Environmental irritants & bronchitis

Exposure to substances that can irritate your bronchial tubes can also increase your risk of developing acute bronchitis, as well as worsening the symptoms of both acute and chronic bronchitis. Over time, if repeatedly exposed to irritants, damage to your lungs and airway tissue can be caused, which could lead to chronic bronchitis.

Common environmental irritants include air pollution and dust. Studies have found that children are particularly susceptible to the effects of air pollution, which can increase the risk of acute bronchitis in young children exposed to nitrogen oxides in the air.3


1. Can Fam Physician. 2008 Feb; 54(2): 238–239. {}

2.Mayo Clinic, Bronchitis {}

3. Ambient nitrogen oxides exposure and early childhood respiratory illnesses, Environment International
Volume 39, Issue 1, February 2012, Pages 96-102 {}

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