Can Allergies Cause Green Phlegm?

Key takeaways:

• Phlegm from allergies is usually clear, but mild infections can cause green phlegm without other symptoms.
• Green phlegm often indicates a bacterial or viral infection and may require treatment.
• See a doctor if green phlegm persists, worsens, or comes with severe symptoms like fever or difficulty breathing.

Phlegm (sputum) is produced by irritated airway cells. These cells reside in our nose, throat, airway passages, and lungs. Anything that irritates these cells will cause them to produce sputum or phlegm. This mucus-like material is frequently coughed or spit up. At times, the color of phlegm can tell us what is causing our symptoms. Green phlegm often indicates infection, either with bacteria or viruses. The green color comes from substances our immune system makes while fighting infection. In allergic conditions, there are no viruses or bacteria present. So there should not be green sputum. However, this can vary from patient to patient. It may also be that only a mild infection is present. This could trigger green phlegm production without causing other symptoms.

The link between allergies and green phlegm

Allergies cause phlegm production because of airway irritation. This can extend from the nose and throat into our lungs. Phlegm as a result of allergic irritation is usually colorless. This isn't always the case, however.

Symptoms to differentiate allergies from other causes

The presence of other symptoms can help determine what the cause is.

Signs the green phlegm is likely to be from allergies

Allergies often lead to runny nose or congestion, sneezing, and mucus dripping down the throat from the nose. This is called post-nasal drip. There may also be a seasonal component to your symptoms. You may be affected during certain times of the year, like fall or spring. This would point toward an allergic cause to your symptoms.

This mucus that drips down the throat can also cause us to cough. While the mucus in allergic conditions is usually clear, this is not always true. It can be difficult to assess mucus color.

Signs the green phlegm may be caused by another condition

If you are experiencing fever, chills, fatigue, or body aches, you may have an infection. Upper respiratory infections with viruses or bacteria can cause all these and green phlegm.

When green phlegm is caused by another condition

There are times when other conditions cause green sputum.

Chronic bronchitis

Chronic bronchitis is a condition classified as a kind of chronic obstructive pulmonary disease (COPD). It is defined as a productive cough lasting more than three months. A “productive” cough produces phlegm.

There are many causes of chronic bronchitis. One of the most common is exposure to cigarette smoke. This can be due to active or passive (second-hand) smoke inhalation. Constant exposure to smog, chemicals, or industrial pollutants can also cause chronic bronchitis. Chronic acid reflux is another rare cause.

Chronic bronchitis symptoms include productive cough, fatigue, and chest or abdominal pain (from excessive coughing). The phlegm color in chronic bronchitis can range from white to yellow or green. This is influenced by many factors. One factor is the presence or absence of infection.

Patients with chronic bronchitis have chronically inflamed airways. The inflammation causes mucus production. This inflammation also makes the lungs more susceptible to infection. Viral or bacterial infection in patients with chronic bronchitis is common. This infection will lead to changes in the color (and sometimes thickness) of the phlegm produced.

Lung abscess

There are occasions when a severe lung infection leads to green phlegm production. This is known as a lung abscess. In a lung abscess, there is a collection of infected fluid in and/or around the lung.

There are multiple causes of lung abscess. These are classified as primary or secondary (from other causes). The cause of a primary lung abscess is fluid or saliva in the mouth and throat getting trapped in the lungs. This is known as aspiration. Patients with altered levels of consciousness, such as a coma or intoxication, are prone to this.

Secondary lung abscesses result from other causes such as tumors, lung diseases, or injuries. In either case, a lung abscess can cause a cough with green phlegm. Other symptoms include fever, chills, night sweats, and chest pain.

Cystic fibrosis

Cystic fibrosis is a chronic disease that leads to frequent sinus and lung infections. It is caused by a genetic mutation. Because of this mutation, mucus builds up in the lungs and frequently the pancreas. This mucus is thick and difficult to clear. It plugs up the airways and allows bacteria to thrive.

Symptoms of cystic fibrosis include chronic cough with thick mucus. The mucus is often green. This is due to the bacteria growing in the lungs.

There can be many additional symptoms of cystic fibrosis. It is a complex genetic disorder that affects many organ systems. It is usually diagnosed at birth as part of a screening program. There are times when it is not diagnosed until later in life.

When you should see a doctor for green phlegm

It is reasonable to monitor your symptoms at home for one or two days. If, however, your symptoms are severe or don’t improve, see your doctor.

You should see a doctor if:

• You have a fever (temperature greater than 100.4 degrees Fahrenheit).
• Your symptoms don’t improve after 48 hours.
• Your symptoms are severe.

You should go to the emergency room if:

• You have trouble breathing or are breathing rapidly.
• If you are drooling because you can’t swallow your saliva (spit).
• Your neck or tongue is swollen.
• You can’t open your mouth or move your neck.

Questions to ask your doctor about green phlegm

• What is causing these symptoms?
• Can I do anything at home for them?
• Am I contagious?
• How long will this last?

Diagnosing green phlegm

Green phlegm can indicate the presence of infection. So your doctor may want to check labs, which can be helpful in looking for an infection. You may need to provide a sample of your phlegm for analysis. It can be checked for bacteria or other substances that indicate infection. Further, your doctor may want an x-ray of your chest. At times, a CT scan may even be helpful.

How a doctor can help treat green phlegm

Treating your green phlegm will depend on the cause.

Antibiotics

A doctor prescribes antibiotics if your symptoms are caused by a bacterial infection or bacterial pneumonia. It is important to take them exactly as prescribed. If you stop them early, your infection can return and get worse.

Anti-allergy medications

If your green phlegm is because of an allergic reaction, your doctor may recommend medication. This can be over-the-counter or prescription. Take the medication as prescribed, even if you feel better.

Managing green phlegm and allergies

If you have a cough with green phlegm, it is okay to monitor your symptoms at home for one or two days. If your symptoms persist longer than that or are severe, please call your doctor.

General Medicine follows a strict editorial process, including using real experts to write our articles, vetted primary sources, fact-checking, a secondary medical review, and updates as necessary. This article was medically reviewed and fact checked by Dr. Jennifer Nadel, MD.

Sources

Rogers, Duncan F. “Physiology of airway mucus secretion and pathophysiology of hypersecretion.” Respiratory care vol. 52,9 (2007): 1134-46; discussion 1146-9. https://rc.rcjournal.com/content/52/9/1134.short.

Akhouri, Shweta, and Steven A. House. “Allergic Rhinitis.” PubMed, StatPearls Publishing, 2023, www.ncbi.nlm.nih.gov/books/NBK538186/.

Thomas, Micah, and Paul A Bomar. “Upper Respiratory Tract Infection.” National Library of Medicine, StatPearls Publishing, 26 June 2023, www.ncbi.nlm.nih.gov/books/NBK532961/.

Pfennig, Camiron L., and B. Ethan Brown. “Sputum.” Access Medicine, McGraw-Hill, 2021, accessmedicine.mhmedical.com/content.aspx?bookid=2969§ionid=250464512.

Widysanto, Allen, and George Mathew. “Chronic Bronchitis.” National Library of Medicine, StatPearls Publishing, 28 Nov. 2022, www.ncbi.nlm.nih.gov/books/NBK482437/.

Sabbula, Bhanusivakumar R., et al. “Lung Abscess.” PubMed, StatPearls Publishing, 2020, www.ncbi.nlm.nih.gov/books/NBK555920/.

Yu, Elaine, and Sandeep Sharma. “Cystic Fibrosis.” National Library of Medicine, StatPearls Publishing, 8 Aug. 2022, www.ncbi.nlm.nih.gov/books/NBK493206/.