How to differentiate the causes of white phlegm in cough

In general, the causes of white phlegm in cough can be differentiated by associated symptoms, sputum characteristics, timing of episodes, triggering factors, duration of illness, and other aspects. The specific analysis is as follows:

1. Associated Symptoms

If accompanied by nasal congestion, runny nose, or sore throat, it is usually caused by the common cold, as viral irritation of the respiratory mucosa increases secretions leading to white phlegm. If wheezing and chest tightness are present, asthma may be the cause—airway spasms increase mucus production. If fatigue and shortness of breath occur alongside, heart failure should be considered, as pulmonary congestion promotes the production of white phlegm.

2. Sputum Characteristics

White frothy sputum is commonly seen in heart failure and chronic bronchitis, typically thin with abundant foam. White viscous sputum may indicate chronic pharyngitis or mycoplasma infection, characterized by higher viscosity and difficulty in expectoration. Stringy white sputum that can be stretched into fine threads is often associated with fungal infections.

3. Timing of Episodes

Worsening of white phlegm upon waking may suggest chronic bronchitis, due to accumulation of respiratory secretions during sleep that stimulate coughing in the morning. Increased coughing with white phlegm when lying flat at night is commonly seen in heart failure, as pulmonary congestion worsens in supine position, promoting sputum production. Cough with white phlegm after exercise is often due to exercise-induced asthma, where physical activity triggers airway responsiveness.

4. Triggering Factors

Cough with white phlegm triggered by cold air may indicate airway hyperresponsiveness, as cold air irritates the respiratory mucosa. Onset following exposure to dust or cooking fumes suggests chronic pharyngitis or bronchitis, where foreign particles irritate the airways and induce white sputum. Symptoms appearing after exposure to pollen or house dust mites may point to allergic cough, in which hypersensitivity reactions lead to increased mucosal secretions.

5. Duration of Illness

A course of illness shorter than 3 weeks is typically acute infection, such as the common cold or acute bronchitis; symptoms usually resolve once the infection is controlled. A duration exceeding 8 weeks may indicate a chronic condition, such as chronic bronchitis or asthma, requiring long-term management and treatment.

In addition, identifying the cause of cough with white phlegm can also take into account past medical history and overall health status. If symptoms persist or worsen, timely medical evaluation is essential to determine the underlying cause and prevent delayed treatment.