Phlegm is thick mucus produced in the lower respiratory tract in response to inflammation or irritation. Unlike the thin, clear mucus that continually lines the nasal passages and throat, phlegm is typically noticed only when excess amounts accumulate or are coughed up. Phlegm acts as a sticky barrier to trap inhaled foreign particles, such as dust, bacteria, and viruses, preventing them from entering the delicate lung tissue. Once irritants are trapped, tiny hair-like structures called cilia move the phlegm up the airways so it can be expelled from the body.
Phlegm Due to Short-Term Illness
A common cause of increased throat phlegm is an acute infection, where the body deploys immune defenses against a pathogen. Viral infections, such as the common cold or influenza, cause inflammation in the respiratory lining, prompting cells to produce more mucus and water to flush out invaders. This phlegm is initially often clear or white, reflecting the body’s early response.
As the illness progresses, the phlegm color frequently changes due to immune system activity. When white blood cells rush to the site of infection, the presence of these dead immune cells and inflammatory debris can turn the phlegm yellow or green. This color change is a sign of an active immune response, though it does not definitively prove a bacterial infection. Acute conditions like bronchitis or sinusitis may also lead to this temporary, colored phlegm that generally resolves as the body clears the infection.
Phlegm Triggered by Allergies and Irritants
Environmental exposure can trigger phlegm production by stimulating the immune system or mechanically irritating the airways. In cases of allergic rhinitis (hay fever), the immune system overreacts to harmless substances like pollen or pet dander. This reaction releases chemicals such as histamine, causing inflammation and increasing mucus production in the nasal passages. This often manifests as a clear, thin post-nasal drip that irritates the throat.
Non-allergic irritants, such as tobacco smoke, air pollution, or strong chemicals, cause mechanical irritation to the airway linings. The delicate tissues respond by generating extra phlegm to trap and clear these toxins. This excess mucus is often clear or white. Unlike temporary infectious phlegm, this production continues as long as the environmental exposure is present.
Non-Respiratory System Causes
Sometimes, the source of throat phlegm originates outside of the respiratory tract, such as with Laryngopharyngeal Reflux (LPR). LPR is a form of acid reflux, often called “silent reflux,” where stomach contents travel up the esophagus and irritate the delicate tissue of the throat and larynx. This irritation occurs because the upper esophageal sphincter fails to prevent the backflow from reaching the upper airway.
The throat tissue, which is not designed to withstand stomach acid, reacts to the chemical burn by producing excessive, thick mucus as a protective barrier. This phlegm is typically white and is often accompanied by the sensation of a lump in the throat, a persistent need to clear the throat, or chronic hoarseness. The reflux usually occurs when a person is upright or during the day, differentiating it from typical nighttime GERD symptoms.
Seeking Professional Evaluation
While most cases of increased throat phlegm are temporary, certain symptoms warrant a professional medical evaluation. If the phlegm persists for an extended period, such as longer than four weeks, despite addressing common causes, it may indicate a chronic or underlying issue.
Immediate medical attention is necessary if the phlegm contains blood, as this can be a sign of a serious condition affecting the lungs or airways. A doctor should also be consulted if the phlegm is accompanied by:
- A high or persistent fever
- Chest pain or difficulty breathing
- Unexplained weight loss
- New or worsening wheezing
- Difficulty swallowing