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If you have bronchitis, the lining of the airways in your lungs gets inflamed. This makes you cough. Almost all cases of bronchitis are caused by infection with a virus.

Bronchitis doesn't tend to be serious for people who are normally healthy. It usually goes away on its own, even without treatment. But if your symptoms are very bad, your doctor may want to do tests to make sure you don't have a more serious illness, such as pneumonia.¹

Bronchitis that lasts up to three weeks is called acute bronchitis.² If your symptoms last more than three weeks, your doctor might call your condition persistent bronchitis. If you cough up mucus every day for at least three months, two years in a row, it's called chronic bronchitis.²

This information covers acute bronchitis.

There are lots of different viruses that can cause bronchitis. Doctors think flu (influenza) viruses are one of the most common causes.² Cold viruses can also lead to bronchitis.³ Bronchitis often starts as you're just getting over another illness, such as the flu.

Viruses spread easily from one to person to another. For example, you can breathe in viruses when you stand next to someone who has just coughed. As your body fights off the virus, it makes the lining of your lungs' airways inflamed and coated with mucus. This causes the symptoms of bronchitis. Bacteria rarely cause bronchitis.³

Some other things can damage the lining of your lungs and lead to bronchitis. Breathing in a lot of chemical fumes or smoke from a fire may do this.³

Air pollution can also trigger bronchitis, especially if you already have another condition that affects your heart or lungs.⁴ Dust from animals and plant farming, mining and working with stone can lead to bronchitis. However, it usually takes many years for this type of lung damage to happen. It usually causes long-lasting (chronic) bronchitis, not acute bronchitis.

If you smoke, you're at increased risk of getting chronic bronchitis.^{5 6} But researchers aren't sure if smoking increases your chances of getting a bout of acute bronchitis. To read more about chronic bronchitis, see Chronic obstructive pulmonary disease.

Children under 4 and older people are most likely to get bronchitis, especially if they already have other health problems that affect their lungs and heart.⁷

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.