Coughing up white phlegm may indicate bronchitis that is viral in nature, explains Cedars-Sinai. It can also be a sign of mycoplasmatic pneumonia, which shares characteristics of both viral and bacterial types of pneumonia, states University of Pittsburgh Medical Center. A third possibility is heart failure, notes Harvard Health Publications.
Coughing is typically the final symptom to clear up in patients with bronchitis that develops as a result of an infection, notes Cedars-Sinai. While small amounts of white phlegm suggest viral bronchitis, the mucus may change to a yellow or green color over the course of the illness, potentially signifying that the patient has also developed a bacterial infection. Other common symptoms of bronchitis due to infection are a runny nose, sore throat, chills, fever, fatigue and aches.
Mycoplasmatic pneumonia is a relatively mild form of pneumonia, according to University of Pittsburgh Medical Center. It most commonly affects older children and young adults but can occur in people of all ages. In addition to a cough that produces small amounts of white phlegm, patients with mycoplasmatic pneumonia may present with prolonged weakness, nausea, vomiting, fever and chills.
Patients who cough as a result of heart failure usually experience the worst coughing while lying down on a flat surface, explains Harvard Health Publications. If the coughing produces white mucus, it is frothy and thin, although these patients may also exhibit dry coughing.