Bronchitis happens when the airways leading to your lungs become irritated, swollen, and filled with mucus. In most cases, you get it the same way you catch a cold: a virus enters your body through your nose, mouth, or eyes. But there are two distinct forms of bronchitis, and they develop in very different ways.
Acute Bronchitis: A Viral Infection
Acute bronchitis is almost always caused by a virus. The same viruses that give you colds and the flu can travel deeper into your respiratory tract and inflame the bronchial tubes, the large airways that carry air into your lungs. When that lining gets irritated, your immune system triggers swelling and ramps up mucus production, which is what causes the persistent cough.
You catch these viruses the same way you catch a cold. An infected person coughs or sneezes, sending tiny droplets into the air that can land in your mouth or nose or be inhaled into your lungs. You can also pick up the virus by touching a contaminated surface, like a doorknob or railing, and then touching your face. Because many different viruses can cause it, and all of them are highly contagious, acute bronchitis is extremely common.
Acute bronchitis typically clears up on its own within a few weeks. Antibiotics don’t help in the vast majority of cases. The CDC specifically recommends against routine antibiotic treatment for uncomplicated acute bronchitis, regardless of how long the cough lasts. Colored or yellow-green mucus does not mean you have a bacterial infection, despite what many people assume.
Chronic Bronchitis: Long-Term Irritation
Chronic bronchitis is a fundamentally different condition. Rather than a short-lived infection, it’s a persistent inflammation of the bronchial lining caused by ongoing exposure to irritants. The most common cause, by a wide margin, is cigarette smoking.
To qualify as chronic bronchitis, you need to have a mucus-producing cough most days of the month for at least three months, and that pattern has to repeat over at least two years. It’s not something you “catch.” It develops gradually as repeated irritation reshapes the airway lining. The cells that produce mucus multiply and enlarge, a process called goblet cell metaplasia, and the airways begin secreting far more mucus than the body can clear efficiently.
When mucus builds up faster than the airways can flush it out, it becomes thick and concentrated. Sticky mucus plaques form along the airway walls, trapping bacteria and reducing oxygen flow. That low-oxygen environment triggers further immune responses: the body releases inflammatory signals that, paradoxically, stimulate even more mucus production without enough fluid to thin it out. This creates a self-reinforcing cycle of inflammation, mucus buildup, and tissue damage.
Smoke and Other Airway Irritants
Cigarette smoke is the leading cause of chronic bronchitis, but it’s not the only irritant that can inflame your airways. Secondhand smoke, air pollution, and dust or toxic gases in your environment all contribute. Some irritants can also trigger acute bronchitis episodes in people who don’t have the chronic form.
Workplace exposures deserve special attention. Industrial bronchitis develops in people regularly exposed to specific dusts and fumes. The list of known triggers includes coal dust, asbestos, silica, cotton fibers, metal particles, latex, and chemical compounds like toluene diisocyanate (used in foam and coating manufacturing). Western red cedar dust is another well-documented cause. If you work in mining, textiles, manufacturing, or construction, prolonged exposure to these materials can cause the same kind of airway inflammation that smoking does.
What Happens Inside Your Airways
Whether the trigger is a virus or years of cigarette smoke, the basic mechanism is similar. Your bronchial tubes are lined with cells that produce a thin layer of mucus, which normally traps dust and germs so tiny hair-like structures called cilia can sweep them out. When something irritates that lining, the immune system kicks off a chain reaction.
The airway walls swell, narrowing the space air passes through. Mucus-producing cells go into overdrive, flooding the airways with thick secretions. In acute bronchitis, this process is temporary. Your body fights off the virus, the swelling subsides, and mucus production returns to normal. In chronic bronchitis, the irritation never stops. The airway lining physically remodels itself, with more mucus-producing cells replacing normal tissue. Inflammatory immune cells, particularly neutrophils, accumulate in the airways and release enzymes that further stimulate mucus secretion and damage the bronchial walls.
Bacteria trapped in thick mucus plaques consume oxygen, creating pockets of low oxygen along the airway surface. The body responds by releasing more inflammatory signals, which drive more mucus production, which traps more bacteria. Breaking this cycle is why quitting smoking is the single most effective treatment for chronic bronchitis.
Who Is Most Likely to Get It
Almost everyone gets acute bronchitis at some point. It peaks during cold and flu season and is more common in young children and older adults. You’re at higher risk if you’re around someone who’s sick, if your immune system is weakened, or if you’re frequently in crowded spaces during respiratory virus season.
Chronic bronchitis has a more specific risk profile. Current and former smokers carry the highest risk. People exposed to occupational dusts and fumes over years are also vulnerable, especially if workplace ventilation is poor. Living in areas with high air pollution adds another layer of risk. Some people develop recurrent acute bronchitis episodes that are frequent enough to meet the threshold for a chronic diagnosis.
When Bronchitis Gets Worse
Most acute bronchitis resolves without complications, but in some cases, the infection can spread deeper into the lungs and develop into pneumonia. Warning signs include a fever above 100.4°F (38°C), a heart rate consistently above 100 beats per minute, rapid breathing (24 or more breaths per minute), and a change in lung sounds that a doctor can detect during an exam. These signs help distinguish a simple bronchitis cough from something more serious, since bronchitis alone rarely causes abnormal vital signs in otherwise healthy adults.
For people with chronic bronchitis, catching a viral respiratory infection on top of already-damaged airways can trigger a flare-up, sometimes called an acute exacerbation. These episodes can be significantly more severe than a typical cold and may require medical treatment to manage the sudden worsening of symptoms.