Causes and Risk Factors of Bronchitis

Table of Contents
View All
Table of Contents

Bronchitis is caused by inflammation of the bronchi, which are the passages that air travels through when you breathe in and out.

Short-term inflammation of the bronchi, which is defined as acute bronchitis, is usually triggered by an infection. Long-term inflammation of the bronchi, which is defined as chronic bronchitis, is caused by recurrent inflammation of the bronchi, usually as a result of smoking or other inhaled irritants.

bronchitis causes and risk factors
© Verywell, 2018

Common Causes 

The inflammation of acute and chronic bronchitis prevents air from traveling in and out of the lungs efficiently. Air must travel through the bronchi before reaching the lungs. With bronchitis, these passageways are not clear and wide as they should be. Instead, the bronchi become filled with inflammatory material, which is primarily composed of a combination of immune cells and mucus.

The resulting bronchial obstruction is why people who have bronchitis may experience wheezing and shortness of breath.

A cough is the body’s attempt to rid itself of irritants in the respiratory system.

Both acute and chronic bronchitis are characterized by inflammation that obstructs air passageways. The triggers that cause inflammation may be different in acute bronchitis and chronic bronchitis.

Acute Bronchitis 

Acute bronchitis is normally caused by an infection that involves the bronchi. The most common ones are viral infections. Bacterial infections are a relatively uncommon cause of acute bronchitis and fungal infections of the respiratory system are a rare cause of acute bronchitis.

These can happen if you have an infection that lingers, if you have recurrent infections within a short period of time, or if your immune system is weak. Often there is no clear explanation for why a respiratory infection involves the bronchi, and having acute bronchitis does not mean that your immune system is weak.

Acute bronchitis may also occur if you have had single or recurrent short-term exposure to environmental inhalants, such as from fumes or chemicals that could trigger an inflammatory reaction.

Chronic Bronchitis 

Chronic bronchitis develops over time. Often, bronchi become damaged when exposed to inhaled chemicals because the chemicals require passage through the bronchi. This produces an inflammatory reaction of the bronchi. Inflammation continues and builds up over time, resulting in the persistent presence of mucus, inflammatory cells, and possibly narrowing or stiffening.

Smoking, which irritates the bronchi, is the most common cause of chronic bronchitis, but long-term exposure to other inhalants can cause it as well. For example, people who breathe in toxic fumes at work can develop chronic bronchitis.

Acute bronchitis is typically not thought to cause chronic bronchitis. If you have chronic bronchitis, you may be more likely to experience exacerbation of your symptoms, such as coughing, wheezing or chest pain, when you have a respiratory infection, and they would be more likely to linger than they would if you did not have chronic bronchitis.


In general, bronchitis is not considered a genetic condition, although there seems to be a weak genetic predisposition to developing acute and chronic bronchitis. Chronic bronchitis, in particular, seems to run in families.

It is not clear whether this is related to shared lifestyle factors, common environmental exposures, or an inborn susceptibility to bronchitis. Numerous studies have attempted to identify genes related to these conditions, but there is no definitive answer regarding a specific gene or inheritance pattern for bronchitis.


There are cardiovascular consequences of severe bronchitis. Cardiovascular disease does not cause bronchitis to develop. Cardiovascular conditions that are associated with shortness of breath, such as heart failure, can make the symptoms of chronic bronchitis, and even acute bronchitis, more disabling.

Congenital diseases of the heart or pulmonary system can, similarly, exacerbate some of the symptoms of bronchitis if bronchitis develops for other reasons.

Lifestyle Risk Factors

There are a number of lifestyle factors that contribute to both chronic and acute bronchitis.

Chronic bronchitis is very strongly related to lifestyle factors.

Long-term repeated exposure to inhaled irritants, whether deliberate or due to circumstance, is the main risk factor of chronic bronchitis.

  • Smoking: Smoking is the leading cause of chronic bronchitis. Cigarettes are still the most commonly smoked product, but pipes and other inhalants and devices through which people smoke are also likely to cause the chronic inflammatory reaction. Each type of substance smoked, whether tobacco or any other material, causes damage to the bronchi, inflammation, mucus buildup, and obstruction.
  • Chemical inhalants: Close and frequent exposure to concentrated inhaled chemicals in the air can cause bronchitis. This is most commonly seen in the work setting. People who may be exposed to such fumes are advised to wear protective gear to minimize the dangers. Of course, financial access to such gear and verification of the quality of protective wear is easier to attain for those who have resources.
  • Pollution: Exposure to pollution, unlike exposure to inhalants in close proximity, affects people who dwell in the vicinity of high levels of pollution. This may be related to chemicals in nearby factories, automobile fumes, waste material, or other systematic issues.
  • Urban environment: Some studies show that people living in urban environments are more likely to be hospitalized for bronchitis. While this may be at least partially related to access to healthcare in urban settings, it appears that the urban settings themselves may put people at a higher risk of bronchitis due to inhalant exposure.

Acute bronchitis

  • Hygiene: The chances of becoming sick with acute bronchitis are increased when you are exposed to bacteria or viruses that cause respiratory infections. While we are all exposed to these types of organisms on a regular basis, steps such as hand washing and avoiding exposure to respiratory droplets through other people’s coughing and sneezing can diminish your chances of getting a respiratory infection that progresses to become acute bronchitis. This is especially important if you have chronic bronchitis, as an acute bout of bronchitis can be especially hard on someone who has chronic bronchitis.

Frequently Asked Questions

  • What happens in your body when you have bronchitis?

    Bronchitis occurs when the tissue that lines the bronchi, the tubes that lead to the lungs, becomes inflamed due to an infection or irritant such as cigarette smoke. This causes the airways to become inflamed and swollen. In response, cells in the lining of the bronchi produce mucus to try to protect the airways. However, the accumulation of the mucus plus the swelling of the bronchi restricts the flow of air to and from the lungs.

  • Why do you cough up phlegm when you have bronchitis?

    Also known as sputum, phlegm is the mucus that accumulates in the airways. In addition to protecting the airways, phlegm traps bacteria and other substances to prevent them from reaching the lungs. Hairlike structures called cilia that line the airways move the phlegm toward the throat, which induces the coughing reflex.

  • Do acute bronchitis and chronic bronchitis have the same cause?

    The single underlying cause of both types of bronchitis is inflammation and swelling of the bronchi and accumulation of mucus in the lining of the bronchi, which together obstruct breathing. A viral or, less often, bacterial infection causes acute bronchitis. Chronic bronchitis results from repeated exposure to an irritant such as cigarette smoke.

  • What makes people wheeze when they have bronchitis?

    Wheezing—a whistling or rattling sound while breathing—is caused by the restriction of air flow in the respiratory tract. Sometimes only a doctor can hear wheezing through a stethoscope, but the noise also can be loud enough to be heard by the human ear. Wheezing most often occurs when someone exhales.

  • Can I get chronic bronchitis from air pollution?

    Although cigarette smoking is the most common cause of chronic bronchitis, studies have shown a definitive link between air pollution and the persistent cough and mucus production characteristic of chronic bronchitis. Types of air pollution associated with chronic bronchitis include automobile fumes, power plant fumes, and indoor wood smoke.

  • Who's at highest risk for chronic bronchitis?

    Chronic bronchitis is most common among people who smoke—especially female smokers. For nonsmokers, the risk factors for chronic bronchitis are:

  • Which viruses and bacteria cause acute bronchitis?

    More than 95% of cases of acute bronchitis result from a viral infection. In people who have health conditions that make them especially vulnerable to infection, bacteria may be the cause.

    Viruse causes include Rhinovirus, Adenovirus, Influenza A or B, Parainfluenza, Respiratory syncytial virus, and Human metapneumovirus. Bacteria causes include Mycoplasma pneumoniae,  Bordetella pertussis,  and Chlamydia pneumoniae.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Heart, Lung, and Blood Institute. Bronchitis.

  2. Centers for Disease Control and Prevention. Chest Cold (Acute Bronchitis).

  3. Bai L, Su X, Zhao D. Exposure to traffic-related air pollution and acute bronchitis in children: season and age as modifiers. J Epidemiol Community Health. 2018 May;72(5):426-433. doi:10.1136/jech-2017-209948

  4. Raju SV, Tate JH, Peacock SK. Impact of heterozygote CFTR mutations in COPD patients with chronic bronchitis. Respir Res. 2014 Feb 11;15:18. doi:10.1186/1465-9921-15-18

  5. Wedzicha JA, Brill SE, Allinson JP, Donaldson GC. Mechanisms and impact of the frequent exacerbator phenotype in chronic obstructive pulmonary disease. BMC Med. 2013;11:181. doi:10.1186/1741-7015-11-181

  6. Pleasants RA, Riley IL, Mannino DM. Defining and targeting health disparities in chronic obstructive pulmonary disease. Int J Chron Obstruct Pulmon Dis. 2016;11:2475-2496. doi:10.2147/COPD.S79077

  7. Singh A, Avula A, Zahn E. Acute Bronchitis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

  8. Fahy JV, Dickey BF. Airway mucus function and dysfunctionN Engl J Med. 2010;363(23):2233-2247. doi:10.1056/NEJMra0910061

  9. Cleveland Clinic. Wheezing.

  10. Salameh P, Salame J, Khayat G, et al. Exposure to outdoor air pollution and chronic bronchitis in adults: a case-control studyInt J Occup Environ Med. 2012;3(4):165-177.

  11. Merck Manual Professional Version. Acute bronchitis.

By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.