Modern medicine classifies a cough following an upper respiratory illness as post-infectious cough or post-viral chronic cough. This refers to a cough that persists for more than three weeks even after the inflammation from the viral infection has resolved, and it is not simply caused by the active virus remaining in the body. Instead, it occurs because the immune system remains in a prolonged hypersensitivity reaction after undergoing the stress of an infection.
When a cold virus enters the body, an inflammatory cascade is triggered to eliminate the pathogen. During this process, immune signaling proteins called cytokines are released, which can overstimulate the nerve fibers surrounding the bronchus. In particular, the cough reflex nerves linked to the vagus nerve become sensitized, leading to airway hyperresponsiveness where minor triggers that normally provoke no reaction, such as cold air, dust, low humidity, laughing, or speaking loudly, can induce a cough.
In addition, the bronchial mucosa damaged by the initial infection often remains in a state of chronic low-grade inflammation rather than healing completely. When inflammation persists, the function of bronchial epithelial cells declines, and mucous glands undergo hyperactivation, producing sticky, dry phlegm that perpetuates a cycle of coughing. Clinical research also shows that patients with post-infectious cough exhibit increased expression of transient receptor potential vanilloid 1 receptors in the bronchus, heightening their sensitivity to external stimuli. This receptor plays an essential role in mediating pain, heat sensations, and the cough reflex.
The immune system is also tightly linked to the stress response. If you face chronic stress, sleep deprivation, or an irregular schedule while recovering from an infection, stress hormones such as cortisol are secreted in excess, further impairing immune function. This diminishes the body's ability to regulate inflammation, causing the cough to linger and delaying overall recovery. The concept of lung deficiency described in Donguibogam aligns with what modern medicine recognizes as airway hyperresponsiveness, chronic low-grade inflammation, and neuro-immune dysregulation. Resolving a post-cold cough therefore requires looking beyond symptom suppression to restore balance to both the immune system and the autonomic nervous system.
