Although a cold is an acute respiratory disease caused by a viral infection, its traces can linger long after the virus has left our bodies, specifically in the form of a chronic cough. Modern medicine classifies a cough persisting for more than a month after a cold as a chronic cough, which aligns with the context of illness having settled in the lungs described in the Donguibogam.
When a cold virus invades the lungs and bronchus, our body initiates an inflammatory response to fight the virus. In this process, the bronchial mucosa becomes damaged and hypersensitive. If the inflammatory response does not subside completely or the damaged mucosa does not fully recover even after the virus is cleared, the bronchus continues to react sensitively to stimuli. This is termed bronchial hyperresponsiveness, a state where the cough reflex is readily provoked by minor irritants such as dust, cold air, exhaust fumes, or dry air.
Furthermore, chronic cough can extend beyond a simple issue of the bronchus. Viral infections can also impact our nervous system. In particular, the vagus nerve regulates the sensation and motor function of various internal organs, including the lungs and bronchus. If the vagus nerve becomes hyperactive or sensitized after infection, the cough reflex arc can be continuously stimulated. The cough center in the brain then issues the command to cough even at lower levels of stimulation than usual.
In addition, gastroesophageal reflux disease and upper airway cough syndrome are common causes of chronic cough. Reflux of gastric acid irritating the esophagus, or nasal secretions dripping down the back of the throat, trigger the cough. Just as the Donguibogam described that phlegm-fluid obstructs the lungs, modern medicine similarly views excessive mucus secretion or acid reflux irritating the bronchus as triggers for coughing. This suggests that imbalances in the digestive system or upper respiratory tract, not merely problems of the lungs themselves, can manifest as systemic respiratory symptoms.
More importantly, such chronic cough interacts with psychological stress. When coughing causes insomnia or interferes with daily life, levels of the stress hormone cortisol rise. This suppresses immune function, aggravating inflammatory reactions and further worsening bronchial hyperresponsiveness. The resulting imbalance in the neuroendocrine system firmly cements the cycle of chronic cough. Therefore, chronic cough is not an isolated lung condition, but a disease requiring a comprehensive approach encompassing our immune system, nervous system, digestive system, and even our mental state.
