Bronchitis has two distinct forms, and their causes are very different. Acute bronchitis is almost always triggered by a viral infection, while chronic bronchitis develops over years from repeated exposure to irritants like cigarette smoke or industrial dust. Understanding which type you’re dealing with changes what you can expect and how it’s managed.
Viruses Cause Most Acute Bronchitis
Viruses are responsible for 85% to 95% of acute bronchitis cases in otherwise healthy adults. The most common culprits are rhinovirus (the same virus behind many common colds), influenza A and B, adenovirus, and parainfluenza virus. In most cases, the infection starts in your upper airways, your nose and throat, then spreads down into the bronchial tubes. Once there, the virus inflames the airway lining, which swells and produces excess mucus. That’s the persistent cough.
Because it’s viral, antibiotics won’t help in the vast majority of cases. The cough typically lingers for two to three weeks, sometimes longer, even after the infection itself has cleared. This is because the bronchial lining needs time to heal after the inflammation subsides.
Bacterial Bronchitis Is Uncommon
Bacteria are detected in only 1% to 10% of acute bronchitis cases. When bacteria are involved, the usual suspects are atypical organisms like Mycoplasma pneumoniae and Chlamydophila pneumoniae, both of which were found in less than 1% of sputum samples from adults with an acute cough lasting more than five days.
One exception worth knowing about is Bordetella pertussis, the bacterium behind whooping cough. About 10% of patients who show up with a cough lasting at least two weeks have evidence of a pertussis infection. If your cough is severe, comes in fits, or has lasted more than two weeks without improving, pertussis is one possibility your doctor may consider.
Smoking and Chronic Bronchitis
Chronic bronchitis is defined as a productive cough (meaning you’re coughing up mucus) that lasts at least three months per year for two consecutive years, with no other underlying cause. Smoking is the single biggest driver.
Prolonged exposure to cigarette smoke damages the cells lining your airways in several ways. It triggers immune cells to flood into lung tissue, releasing inflammatory signals that attract even more immune cells. Over time, this chronic inflammation reshapes your airway lining. The cells that produce mucus (goblet cells) multiply and enlarge, while the tiny hair-like structures called cilia, which normally sweep mucus out of your lungs, become damaged and less effective. The result is a cycle: your lungs produce more mucus than normal but can’t clear it efficiently, leading to the constant cough and phlegm that define chronic bronchitis.
Chemicals in cigarette smoke, including acrolein and particulate matter, directly stimulate mucus production. Smoke also reduces airway hydration, making the mucus thicker and harder to cough up. These changes don’t reverse quickly, which is why chronic bronchitis persists even during periods when you feel otherwise well.
Workplace Dust and Chemical Exposure
You don’t have to smoke to develop chronic bronchitis. Long-term exposure to industrial dusts, fumes, and chemical vapors can cause the same kind of airway damage. This is sometimes called industrial bronchitis, and it’s a recognized occupational hazard. Specific exposures that increase risk include asbestos, coal dust, cotton dust, silica, metal particles, latex, and chemicals like toluene diisocyanate (used in manufacturing foams and coatings). Workers exposed to Western red cedar dust are also at elevated risk.
The mechanism is similar to smoking: inhaled particles irritate and inflame the bronchial lining, eventually leading to the same goblet cell overgrowth and mucus overproduction. People who both smoke and work in high-exposure environments face compounded risk.
Air Pollution and Temperature
Outdoor air quality plays a measurable role, particularly for children. A large study tracking nearly 4 million children in Taiwan over a decade found that bronchitis incidence climbed as fine particulate matter (PM2.5) levels rose. The highest rates occurred during cold weather combined with high pollution: 698 cases per day when temperatures dropped below 20°C and PM2.5 exceeded 37 micrograms per cubic meter. When both temperature was warm and air was clean, that number fell to 392 cases per day.
Cold air on its own can irritate airways, and high particulate levels compound the effect by delivering tiny particles deep into the lungs where they trigger inflammation. If you live in an area with poor air quality, this is one reason bronchitis episodes may cluster during winter months.
Acid Reflux and Airway Irritation
Gastroesophageal reflux, commonly known as acid reflux or GERD, is an underappreciated contributor to bronchitis. The issue isn’t just stomach acid splashing into the esophagus. A gaseous, often non-acidic mist can travel upward and get inhaled into the airways, depositing irritants along the entire respiratory tract from the sinuses down to the smaller airways in the lungs.
When this happens repeatedly, it triggers inflammation, excess mucus production, and bronchoconstriction (tightening of the airways). In people with COPD, reflux-driven bronchitis is considered a major contributor to the persistent cough, phlegm, and wheezing that characterize the disease. If you have recurring bronchitis without an obvious cause, especially if you also experience heartburn, throat clearing, or a hoarse voice, reflux may be playing a role.
Genetic Factors
A genetic condition called alpha-1 antitrypsin deficiency makes some people more vulnerable to chronic bronchitis, even without heavy smoking exposure. Alpha-1 antitrypsin is a protein your liver produces to protect your lungs from damage caused by immune cells. When your body doesn’t make enough of it, or makes a defective version, your lungs are less protected from everyday inflammatory wear and tear.
The condition is caused by variants in a gene on chromosome 14. About 95% of people of European descent carry the normal “M” version of this gene, but variants called “S” and “Z” reduce the protein’s effectiveness. People who inherit two Z copies (the ZZ genotype) are at the highest risk. An estimated 253,000 people worldwide have this genotype. Over 40% of people with alpha-1 antitrypsin deficiency have chronic mucus production even if they’ve never smoked. Those who carry just one Z copy and also smoke face higher COPD risk than smokers with normal genes.
Why Children and Adults Differ
Bronchitis looks different depending on age, and the underlying causes shift too. In children, the most clinically relevant form is protracted bacterial bronchitis, defined as a wet cough lasting more than four weeks that resolves with antibiotics. Unlike adult chronic bronchitis, the driving force in children is bacterial infection causing inflammation dominated by a specific type of immune cell called neutrophils. Risk factors for kids include daycare attendance, premature birth, passive smoke exposure, household crowding, and childhood asthma or allergies.
In adults, chronic bronchitis is driven less by active infection and more by long-term structural changes in the airway. The lining remodels over years: normal cells are replaced by flattened, less functional cells, and mucus glands enlarge. Smoking, occupational exposures, and lower socioeconomic status are the traditional risk factors. The distinction matters because treatment approaches differ significantly between children and adults with chronic cough.