What is the primary indicator of bronchitis?

Increased mucus production is the primary indicator of bronchitis because this condition involves inflammation of the bronchial tubes, which are responsible for carrying air to and from the lungs. When these tubes become inflamed, they tend to produce more mucus as a response to the irritation. This overproduction can lead to symptoms such as coughing, which is often the most noticeable symptom associated with bronchitis. The excess mucus can obstruct airflow and lead to difficulty breathing, making it a central characteristic of the condition. Other symptoms like fever, headache, or chest pain may occur but they are not as defining of bronchitis as increased mucus production, which directly reflects the underlying pathological process occurring in the airways.