Bronchitis is a respiratory disease in which the mucus membrane in the lungs' bronchial passages becomes inflamed. As the irritated membrane swells and grows thicker, it narrows or shuts off the tiny airways in the lungs, resulting in coughing spells that may be accompanied by phlegm and breathlessness.
The main symptom of bronchitis is a hacking cough. It is likely that your cough will bring up thick yellow-grey mucus (phlegm), although this does not always happen.
Other symptoms of bronchitis are similar to those of other infections, such as the common cold or sinusitis, and may include:
runny or blocked nose
aches and pains
Acute bronchitis is usually caused by viruses, typically the same viruses that cause colds and flu (influenza). Antibiotics don't kill viruses, so this type of medication isn't useful in most cases of bronchitis.
The most common cause of chronic bronchitis is smoking cigarettes. Air pollution and dust or toxic gases in the environment or workplace also can contribute to the condition.