Bronchitis can be classified into acute bronchitis and chronic bronchitis based on the onset and progression of the condition. Acute bronchitis usually begins suddenly, with generally mild systemic symptoms. It can include fever and is mostly characterized by a dry cough or a small amount of mucous sputum. Over time, the amount of sputum may increase and the coughing may intensify, occasionally accompanied by blood-streaked sputum. There is generally no significant hemoptysis or chest pain. The duration of cough and expectoration can be quite long, potentially lasting two to three weeks. A small portion of patients may experience prolonged symptoms, eventually progressing to chronic bronchitis. The most common symptoms of chronic bronchitis are also cough and expectoration, but these symptoms last much longer, typically persisting for more than two years and occurring for three months each year. A small number of bronchitis patients may experience bronchial spasms or bronchial asthma, leading to varying degrees of chest tightness, shortness of breath, or wheezing.