Common causes of a cough accompanied by clear mucus include a viral illness, infection, chronic lung disease and nasal discharge, according to WebMD. Other causes are stomach acid that has backed up into the esophagus and smoking.
A cough that produces phlegm is referred to as a productive cough. Mucus from a productive cough may come down from the nose or up from the lungs, explains WebMD. A productive cough is often a symptom of a common cold, and because this type of cough helps clear mucus from the body, it should not be suppressed. Types of infections that are associated with a productive cough include pneumonia, bronchitis, sinusitis and tuberculosis.
Chronic obstructive pulmonary disease is a type of lung disease that makes breathing difficult, WebMD notes. A combination of chronic bronchitis and emphysema commonly causes this disease. A productive cough may indicate that the COPD is becoming worse, states WebMD. This condition also creates serious symptoms such as severe shortness of breath and heart problems that develop over time .
Coughing caused by a stomach acid build up in the esophagus may be a symptom of gastrointestinal reflux disease, WebMD says. In addition to a productive cough, nasal discharge may cause a feeling that the throat constantly needs to be cleared.