Bronchitis usually starts with a viral infection in your upper respiratory tract that moves down into your lungs

Most acute bronchitis begins when a cold or flu virus spreads from your nose and throat into the tubes that carry air to your lungs (the bronchi). Your body's immune response to the virus causes inflammation and mucus buildup in those tubes, which triggers the cough that defines bronchitis. This typically happens within a few days of catching a respiratory virus.

The viruses that cause bronchitis are the same ones behind common colds and influenza. They spread through respiratory droplets when an infected person coughs, sneezes, or talks near you. You can also catch them by touching a contaminated surface and then touching your face. Once the virus settles in your bronchi, it takes time for your body to clear it — usually one to three weeks, though the cough can linger longer.

Key Takeaways

  • Acute bronchitis is almost always caused by a virus (cold, flu, or other respiratory virus) that spreads to your lungs.
  • Chronic bronchitis develops over years from smoking or long-term exposure to irritants like air pollution or occupational dust.
  • Risk factors that make bronchitis more likely include smoking, recent respiratory infection, weakened immunity, and exposure to secondhand smoke or air pollution.
  • Bronchitis is not contagious itself, but the underlying virus is — you can spread it to others for several days after symptoms start.

How viral infection leads to bronchitis

When you inhale a respiratory virus, it attaches to cells lining your nose, throat, and bronchi. Your immune system recognizes the threat and sends white blood cells to fight it. This immune response causes the tissue to swell and produce extra mucus — your body's attempt to trap and expel the virus. The result is inflammation in the bronchi, which narrows the airways and triggers coughing.

The cough is actually your body's defense mechanism. It tries to clear the mucus and irritation from your airways. Early on, the cough is usually dry. As inflammation continues, your bronchi produce more mucus, and the cough becomes wet (productive), bringing up phlegm or sputum. This phase typically lasts one to two weeks, though some people cough for several weeks after the infection clears.

Chronic bronchitis: how repeated irritation damages your lungs

Chronic bronchitis develops differently — not from a single infection, but from years of exposure to irritants that damage the bronchi. Smoking is the primary cause. Each cigarette exposes your bronchi to thousands of chemicals that inflame the tissue and trigger mucus production. Over time, this repeated injury thickens the bronchial walls, narrows the airways, and damages the tiny hair-like structures (cilia) that normally sweep mucus out of your lungs.

Once the damage is done, your bronchi stay inflamed and produce excess mucus even when you are not fighting an infection. This is why chronic bronchitis is defined by a persistent cough that lasts at least three months per year for two consecutive years. Chronic bronchitis is actually a form of chronic obstructive pulmonary disease (COPD) and is not reversible, though quitting smoking can stop it from getting worse.

Long-term exposure to other irritants can also cause chronic bronchitis. Occupational dust (in mining, construction, or textile work), air pollution, and secondhand smoke are all risk factors. The mechanism is the same: repeated irritation leads to permanent changes in the bronchi.

Who is at higher risk for bronchitis

Certain people are more likely to develop bronchitis after a respiratory infection. Smokers are at much higher risk for both acute and chronic forms. People with weakened immune systems — from HIV, cancer treatment, or immunosuppressive medications — take longer to clear viral infections and are more vulnerable to complications. Very young children and adults over 65 also have less robust immune responses and are at higher risk.

People with existing lung disease, heart disease, or asthma are more likely to develop bronchitis when they catch a respiratory virus. Exposure to air pollution, secondhand smoke, or occupational irritants increases your baseline inflammation and makes your bronchi more reactive. Pregnancy can also increase risk slightly, as immune changes during pregnancy make some women more susceptible to respiratory infections.

Recent illness is a major risk factor. If you have just recovered from a cold or flu, your respiratory tract is already inflamed and your immune system is focused on that infection. A second virus can move into your bronchi more easily during this window.

Environmental and occupational exposures that trigger bronchitis

You do not need a virus to develop bronchitis-like symptoms. Exposure to irritating substances can inflame your bronchi directly. Air pollution, especially particulate matter and ozone, can trigger acute bronchitis in people without underlying lung disease. Chemical fumes, chlorine gas, and other workplace exposures can do the same. People who work in agriculture, mining, construction, or textile manufacturing face chronic exposure to dust and fibers that damage the bronchi over time.

Secondhand smoke is a significant risk factor, especially for children. Exposure to smoke irritates the bronchi and makes viral infections more likely to progress to bronchitis. Indoor air quality matters too — mold, pet dander, and dust mites can trigger inflammation in people with sensitive airways, though this is more commonly associated with asthma than bronchitis.

Why some people get bronchitis after a cold and others do not

The same cold virus affects different people differently. Whether bronchitis develops depends on several factors: how much virus you were exposed to, your immune system's strength, whether your bronchi are already inflamed from smoking or other irritants, and your age. Someone with healthy lungs and a strong immune system might clear the virus from their upper respiratory tract before it reaches the bronchi. Someone with compromised immunity or existing lung irritation may not.

Genetics also play a role. Some people's immune systems mount a stronger inflammatory response to respiratory viruses, which can actually increase the risk of bronchitis. Others have genetic variations that affect how well their cilia clear mucus, making them more prone to infection spreading to the bronchi. This is why bronchitis runs in some families.

The difference between catching bronchitis and developing it

Bronchitis itself is not contagious — you cannot catch bronchitis from someone else. What you can catch is the virus that causes it. If you are exposed to someone with a cold or flu virus, you might develop that infection. Whether it progresses to bronchitis depends on your individual risk factors and immune response. Two people exposed to the same virus may have very different outcomes: one gets a mild cold, the other develops bronchitis.

This distinction matters for prevention. You cannot prevent bronchitis directly, but you can reduce your risk by avoiding respiratory viruses (handwashing, staying away from sick people during cold and flu season), not smoking, and protecting your lungs from occupational or environmental irritants. If you do catch a respiratory infection, managing it early — resting, staying hydrated, and monitoring your symptoms — may help prevent it from progressing to bronchitis.

Frequently Asked Questions

Can you get bronchitis without having a cold first?

Yes. Chronic bronchitis develops from years of irritant exposure without any single infection. Acute bronchitis can also develop from direct exposure to irritating chemicals or air pollution, though viral infection is the most common cause. Some people develop bronchitis-like symptoms from severe allergies or asthma flare-ups.

How long after catching a cold does bronchitis usually start?

Bronchitis typically develops within three to seven days of cold symptoms starting. The virus first causes upper respiratory symptoms (sore throat, runny nose, sneezing), then moves down into the bronchi. Some people develop both upper and lower respiratory symptoms at the same time.

Is bronchitis contagious if I have it?

Bronchitis itself is not contagious, but the virus causing it is. You can spread the underlying virus to others for several days after your symptoms start, even before you develop a cough. Once you have had bronchitis for more than a week, you are less likely to transmit the virus, though you may still be coughing.

Why do some smokers get bronchitis and others do not?

All smokers have chronic inflammation in their bronchi, but not all develop the persistent cough that defines chronic bronchitis. Genetics, the number of cigarettes smoked, duration of smoking, and exposure to other irritants all influence whether chronic bronchitis develops. Some smokers also have better-functioning cilia or stronger immune responses that slow the damage.

Can you get bronchitis more than once?

Yes. Acute bronchitis can develop each time you catch a respiratory virus, especially if you are at higher risk. People with chronic bronchitis have persistent inflammation, so they may experience flare-ups when they catch a new infection on top of their baseline condition.