Coughing Up Phlegm? Here's What to Know (2025)

Coughing up mucus is often a sign of a respiratory infection, allergies, gastroesophageal reflux disease (GERD), or an environmental irritant like smoke or pollution. In some instances, it can be related to a more serious medical condition, including cancer.

Phlegm, the mucus that comes from your respiratory system (also known assputum) is released when you have aproductive cough. The mucus will usually clear on its own as you get over an infection. If you have phlegm and no signs of illness, you should see your healthcare provider for a diagnosis.

Causes

Mucus is a normal part of the respiratory system. It plays an important role in lubricating the airways and defending us against irritants and pathogens.

However, inflammation from various causes results in an increase in mucus production and a thicker consistency. This results in the familiar symptoms of runny nose, congestion, and coughing up phlegm.

Respiratory infections, including COVID-19, are a common cause of inflammation resulting in a productive cough. A dry cough is one of the most common coronavirus symptoms, but coughing up phlegm can also be a symptom of COVID-19.

Bronchitis and pneumonia are two types of infections that typically lead to a productive cough. With bronchitis, the branches of the airways become inflamed and produce thicker mucus. In pneumonia, the lung tissue is infected.

Causes Unrelated to Infection

While infection is a common cause, there are several noninfectious causes of phlegm production, including:

• Allergies: People with allergies often develop postnasal drip (excess mucus leaks down the throat), which can cause them to cough up phlegm.
• GERD: Stomach acid may irritate the throat and voice box, causing a cough with phlegm.
• Cystic fibrosis: An inherited lung condition in which mucus is thick and sticky and clogs airways, it causes a chronic cough with mucus.
• Lung diseases, such as asthma, chronic obstructive lung disease (COPD), and bronchiectasis: Mucus builds up in the lungs and triggers a cough as the body tries to expel the mucus.
• Heart failure: Fluid builds up in the lungs and airways (pulmonary edema), which leads to chronic coughing and mucus.

Some environmental and lifestyle factors can also increase phlegm, such as:

• Smoking: It causes the body to produce thicker mucus and increases the amount of mucus in the airways.
• Relative humidity: Moist, humid air increases allergy symptoms, including increased mucus production.
• Dehydration: One of the body's responses to dehydration is to concentrate and thicken mucus.
• Exposure to air pollution: The body increases mucus production to help expel pollutants when coughing.
• Alcohol use: Because alcohol acts as a diuretic, it can dehydrate the body, which increases mucus production to help counter dryness.

Is Mucus a Sign of Lung Cancer?

Mucus production occurs with certain types of lung cancer. It is a main symptom of invasive mucinous adenocarcinoma (IMA), a less common subtype of lung cancer.

Coughing up mucus, sometimes tinged with blood, can be a sign of other types of lung cancer, but most people also have related symptoms, such as:

• A hoarse voice
• Constant chest pain
• Shortness of breath
• Unexplained weight loss

A productive cough can also be a sign of other cancers, such as thymus cancer affecting a gland in your chest. Thymus tumors are often seen in people diagnosed with myasthenia gravis and other autoimmune disorders.

Coughing also is a symptom of pleural mesothelioma, a cancer of the chest cavity lining often associated with asbestos exposure.

What Does the Color of Phlegm Mean?

While diagnosing the cause of a productive cough does not rely on phlegm color, it can suggest certain causes. Normally, mucus is clear, but phlegm can come in a range of colors that may point to the underlying cause:

• Clear or white phlegm may be seen with allergies, viral infection, underlying lung disease, GERD, and heart failure.
• Green phlegm may be seen with a bacterial infection.
• Pink phlegm suggests fluid in the lungs, known as pulmonary edema, such as in heart failure.
• Red phlegm indicates the presence of blood and may be seen with lung cancer or pulmonary embolism.
• Black phlegm can occur with pollutant exposure, such as from cigarette smoke or air pollution, smoke from fire, or fungal infection.

Treatment

Treating a productive cough depends on the underlying cause. Medications and supportive care at home can help treat a productive cough.

Medications: Treating the underlying cause of a productive cough may include OTC or prescription medications, such as:

• Antibiotics for cough due to bacterial infection, like bacterial pneumonia
• Allergy medications
• Inhalers and corticosteroids for asthma or COPD flares
  
• Diuretics if cough is due to heart failure
• Proton pump inhibitors (PPI) and other medications to treat GERD
• Cough medications which include expectorants and mucolytics (discussed below), and cough suppressants

Home Remedies: Supportive treatment for productive cough includes the following measures to encourage getting rid of phlegm and underlying irritants:

• Drink plenty of fluids
• Use a humidifier
• Take a hot shower
• Try a teaspoon of honey
• Gargle with salt water to loosen phlegm
• Use over-the-counter (OTC) expectorants and mucolytics like Mucinex (guaifenesin)

When to See a Healthcare Provider

If your cough doesn't improve after 10 to 14 days, you should discuss your symptoms with your healthcare provider. Other concerning symptoms should be reported to your healthcare provider for further investigation, such as:

• Difficulty breathing
• Fever, especially if lasting more than four days
• Weight loss
• Coughing up mucus that isn't clear
• Coughing up blood
• Signs of heart failure, such as swollen legs and difficulty breathing when lying flat

Summary

Phlegm is a thick mucus arising in the lower airways in response to lung inflammation or injury. Infection is a common cause, but other conditions like allergies, lung disease, and GERD can cause a productive cough.

Treatment depends on the underlying cause and includes supportive care and medications. Your healthcare provider can help determine the underlying cause and recommend a treatment plan if you are coughing up mucus.