Bronchitis is an inflammation of the lining of the bronchial tubes, which carry air to and from the lungs. It can be either acute or chronic. Acute bronchitis is usually caused by viruses, typically the same viruses that cause colds and flu (influenza) . Chronic bronchitis, on the other hand, is a constant irritation or inflammation of the lining of the bronchial tubes, often due to smoking. The most common symptom of bronchitis is a cough, which may produce discolored mucus or blood. Other symptoms may include chest congestion, wheezing, shortness of breath, sore throat, headache, and low-grade fever. Acute bronchitis usually improves within a week to 10 days without lasting effects, although the cough may linger for weeks. However, if you have repeated bouts of bronchitis, you may have chronic bronchitis, which requires medical attention.