Phlegm Symptoms: Causes

By Shaffer, Michael
By Spader, Catherine RN

What causes phlegm symptoms?

Phlegm is generally associated with diseases, disorders and conditions of the respiratory system, including the nose, throat, windpipe (trachea), bronchial tubes, and lungs, but can also be caused by conditions of the upper digestive tract and the cardiovascular system, such as congestive heart failure.

Phlegm symptoms are commonly caused by bacterial or viral infections of the lungs and upper airways. Healthy lungs are covered with a thin layer of mucus. When threatened by infectious germs or damaging foreign substances, such as smoke or dust, the lungs produce additional mucus. The mucus may thicken and must be expelled from the lungs through coughing in order to keep the airways clear.

In addition, certain foods, particularly dairy products, or medications, such as those for blood pressure, can cause or increase phlegm symptoms. Because there are so many different causes, some of which are life threatening, it is important to contact your doctor or health care practitioner to discuss your symptoms and address your concerns.

Infectious causes of phlegm symptoms

Phlegm symptoms can be caused by various viral and bacterial infections including:

  • Acute bronchitis (inflammation of the bronchial tubes usually caused by a viral infection or sometimes a bacterial infection)

  • Common cold (viral infection)

  • Croup (laryngotracheitis, inflammation of the voice box and windpipe usually caused by a virus)

  • Epiglottitis (rare, life-threatening inflammation of the epiglottis, a flap of cartilage that covers the windpipe and protects it from inhalation of food). Epiglottitis is usually caused by a viral infection and mainly affects infants and children.

  • Influenza (flu)

  • Laryngitis (inflammation of the larynx caused by a viral infection)

  • Pharyngitis (inflammation of the throat usually caused by a viral infection and sometimes a bacterial infection)

  • Pneumonia (lung inflammation, usually caused by a viral or bacterial infection)

  • Sinusitis (inflammation of the sinuses usually due to a viral, bacterial or fungal infection)

  • Tonsillitis (inflammation of the tonsils often caused by an infection)

  • Tuberculosis (serious infection affecting the lungs and other organs)

Other causes of phlegm symptoms

Certain foods and medications as well as a variety of conditions and diseases can cause phlegm buildup. They include:

  • Acid reflux or gastroesophageal reflux disease (GERD; stomach contents leak back into the esophagus and irritate the tissues)

  • Airway irritation or obstruction

  • Asthma and allergies

  • Chronic obstructive pulmonary disease (COPD; a chronic lung disease including emphysema and chronic bronchitis)

  • Congestive heart failure (deterioration of the heart’s ability to pump blood)

  • Consuming dairy products

  • Cystic fibrosis (CF; an inherited disease causing thick, sticky mucus that clogs the lungs, impairs breathing, and enables bacteria to grow)

  • Lung cancer

  • Medications, including those for controlling blood pressure and some types of chemotherapy

  • Pregnancy

  • Pulmonary edema (abnormal fluid buildup in the lungs)

  • Pulmonary embolism (blood clot in the lungs)

  • Smoking

  • Tumor of the larynx (voice box), mouth, or nasopharynx
  • Tumor of the larynx (voice box)

Questions for diagnosing the cause of phlegm symptoms

To aid in diagnosing the cause of your phlegm symptoms, your doctor or licensed health care provider will ask you questions related to your symptoms. Giving complete answers to these questions will help your health care provider in diagnosing the cause of your symptoms. Questions may include:

  • What does your phlegm look like? Is it thick or thin? What color is it?

  • How long have you had the phlegm symptoms?

  • Are you breathing through your mouth (instead of your nose)?

  • Are your phlegm symptoms keeping you up at night?

  • Do you have a fever?

What are the potential complications of phlegm symptoms?

Phlegm symptoms can be caused by an infectious process that may be treated easily. However, some underlying causes of phlegm symptoms can lead to serious complications. It is important to contact your health care provider when you have unexplained phlegm symptoms or if your phlegm is persistent, recurrent, or causes you concern. Once the underlying cause is diagnosed, following the treatment plan you and your doctor design specifically for you can help lower your risk of potential complications including:

  • Anaphylaxis
  • Chronic tonsillitis
  • Dehydration
  • Difficulty sleeping
  • Metastasis (spread of cancer)
  • Organ damage
  • Pulmonary edema
  • Repeated lung infections and damage
  • Respiratory arrest and cardiac arrest
  • Sepsis (blood infection) and septic shock
  • Spread of cancer


  1. What Are the Signs and Symptoms of COPD? American Thoracic Society (ATS).
  2. Collins RD. Differential Diagnosis in Primary Care, 5th ed. Philadelphia: Lippincott, Williams & Williams, 2012.

What are the signs of phlegm problems?

Phlegm is a thick, slippery and sticky substance produced by the throat, bronchial passages, and lungs. Phlegm, also called sputum, contains mucus and sometimes other substances, such as dead cells, pus, or foreign particles, including dust. You may not notice that you produce much phlegm unless you cough due to a respiratory infection, such as pneumonia, or if you have certain other diseases o... Read more about phlegm symptomsintroduction


What other symptoms might occur with phlegm symptoms?

Phlegm symptoms may accompany other symptoms, which vary depending on the underlying disease, disorder or condition. For example, you may have a fever and body aches if your phlegm symptoms are caused by an infection.

Symptoms of an infection that can occur with phlegm symptoms

Infectious ... Read more about phlegm symptomssymptoms

Medical Reviewer: William C. Lloyd III, MD, FACS Last Annual Review Date: Sep 20, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Ear, Nose and Throat

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