Is Green Mucus A Sign Of Infection?

Whether coughed up or dripping from a runny nose, the presence of green mucus is often cause for concern for many otherwise healthy adults and children. Surely it must be a sign of bacterial infection? Why would your otherwise white, healthy and clear mucus change in colour? That is a good question. In this article we will discuss the elements that give mucus, snot and phlegm their colour, which elements predominate in which situations to produce distinct colours, and most importantly what all of this should mean for you and your health.

Natural bodily secretions vary in colour depending on several factors, but the secretions that naturally come out of your body (which are mostly limited to phlegm, snot, and vaginal discharge) should always be clear or white in the healthy state. Green mucus is either caused by pigments produced by bacteria directly, or more often caused by enzymes produced by our white blood cells that fight off against microbes. Either case means infection. 

So it appears your creeping suspicion is well-founded. Your green mucus is most likely caused by infection. But how worried should you be? The answer isn’t very straightforward. It all depends on what symptoms you have, where the mucus is coming from, and whether you have any chronic illnesses or not.

Colour types of mucus

Mucus is essentially a viscous liquid that serves to protect and lubricate your mucosa, which can be thought of as the internal skin covering your digestive, respiratory, and urogenital systems. Excessive mucus produced in the nasal cavity is called snot, and that produced by the lungs is phlegm (or sputum). Mucus in its natural state is clear. White mucus is simply clear mucus in larger quantities that has started to dry up, often indicating excessive mucus.1 White nasal mucus is often the result of early phases of acute rhinosinusitis (an infection of the nasal cavity and sinuses that produces nasal discharge), where inflammation has not yet set in. If white snot turns into green snot, then it’s more likely (though not definitely) that bacterial infection is the culprit rather than viruses. And white phlegm often indicates the production of excess sputum, though this has a wide range of non-infectious causes including COPD and asthma as well.1,2 Any other mucus colour points to the presence of some chromatic (which means colour-giving) particles. 

Green is most often caused by myeloperoxidase. Myeloperoxidase is an enzyme that is the preferred weapon of some of our white blood cells. Some of these cells die in the battle against microbes and myeloperoxidase gets scattered in your mucus.3 And sometimes the microbes themselves carry bacteria such as Pseudomonas aeruginosa.4

Yellow mucus can have more causes. For instance, when that green myeloperoxidase gets old, it can turn yellow. When you get sinusitis or pneumonia, you can often observe that your snot, phlegm, or sputum may turn from white to green and then mature towards a thick yellow secretion.1 But there are other causes. Even large amounts of white snot or phlegm, if present in larger quantities, can turn yellow over time. And when heme, the colourful particle in blood (which is normally red) breaks down, it can turn to a variety of colours, including yellow, which is most commonly seen in bruises.5

Speaking of blood, the heme can also cause varying effects on your mucus colour. Brown mucus is most often caused by pneumonia. Both bacterial and fungal pneumonia can cause your phlegm or sputum to take a brown colour, which is due to old blood.1

And what about black mucus? It turns out some species of black mould are among the same species that cause fungal infection. Coughing up black phlegm can be a symptom of severe fungal pneumonia and should be immediately evaluated by a healthcare professional.1,6 Black sputum can also be caused by long-term exposure to coal dust in miners.7

Effects of green mucus

Green mucus doesn’t have an effect on your health so much as it itself is the effect. It’s the effect of your body fighting off infection. But when your body fights off infection, the change in mucus colour is hardly the only effect you will feel. Whether suffering from the mild effect of the common cold such as a runny nose, feeling the headache of a sinus infection, the cough associated with bronchitis or the fever caused by a more serious chest infection, the symptoms of disease will often go hand-in-hand with the presence of green mucus.1,8

When to determine infection?

The only way to definitively determine infection is through the professional evaluation of a doctor. A doctor will take your symptoms, physical examination, and medical history all into account to determine whether infection is present and if treatment is necessary. Viral infections often resolve on their own and require no treatment at all. Even many bacterial infections, despite being caused by harmful bacteria, often do not require any antibiotics.8,9 And although green mucus strongly points towards infection, yellow snot could also be caused by long standing non-infectious rhinitis caused by seasonal allergy, and yellow phlegm by chronic bronchitis caused by years of smoking.9,10

How to avoid infection?

The best way to avoid infection is to practise disease control. Disease control measures such as wearing personal protective equipment, practising social distancing, regular hand washing and being up-to-date with vaccinations are all highly effective ways to avoid infection. Upper respiratory infections such as the common cold, nonallergic rhinitis, sinusitis, acute bronchitis and even pneumonia are especially easy to prevent this way. The prevention of such infections is especially important in patients with underlying upper respiratory illnesses such as chronic bronchitis, asthma, or chronic sinus infections, as these patients often experience severe symptoms when confronted with such diseases.9,10

When Do You Seek Medical Attention?

If excessive mucus of any colour is coming from your penis or vagina, seek medical attention immediately. These infections can be STIs and must always be evaluated by a professional. Treatment is always necessary, often with powerful antibiotics. Excessive vaginal mucus, even if it’s white mucus, could point to bacterial vaginosis, and although bacterial vaginosis is not an infection per se, it should still be evaluated.11

Brown mucus, and especially black mucus, no matter where they’re coming from, must be evaluated. Severe fungal infections, which are often the culprit of black mucus, may even require emergent surgery and any delay in treatment might prove critical.1

Any discharge coming from the ear, no matter the colour, should also be evaluated. One cause of ear discharge is perforation of the eardrum leading to chronic ear infection. This can lead to life-threatening brain infections and must be duly evaluated.12

And lastly, any discharge in the presence of fever deserves medical attention.8,9

Medication and Ways To Get Rid Of Mucus At Home?

So, you’re producing green phlegm or snot and have none of the red flags mentioned above. You have no fever and no need to get medical attention. Are there any steps you can take to relieve your congestion and get rid of the mucus? The answer is yes! The best way to get rid of mucus is to wash it away. According to the Cleveland clinic, irrigation of the nasal passages with simple saline you can get from pharmacies is one of the best ways to relieve your nose of excess snot and provide temporary relief from a runny nose.13 Mayo clinic suggests the use of applicants for this purpose, the most common of which is the neti pot, though care must be taken to ensure that irrigation is done in sterile conditions.14 

And in cases where you need to seek medical attention, your doctor will provide you with the optimal treatment you need. Cases of viral infection leading to bronchitis, sinusitis, or nonallergic rhinitis that have little impact on your health aside from excess production of phlegm and snot can often be treated symptomatically. More serious conditions, like flair ups of chronic bronchitis, genital infections, or sinus infections that are associated with fever will more likely than not benefit from antibiotics. In case of any doubt, have a visit to your doctor. 


If you have green mucus, whether it’s in the form of snot, phlegm, or something else, chances are, your body is fighting off an infection. But that doesn’t mean that you should rush towards antibiotics. Hopefully by now you are well informed about what your mucus is telling you and can take the most simple of decisions in your hands.


  1. Mucus Color: What Does it Mean? [Internet]. Cleveland Clinic. 2022 [cited 28 September 2022]. Available from:
  2. The Skinny on Snot: What Your Child's Mucus Says About Their Health [Internet]. 2022 [cited 28 September 2022]. Available from:
  3. Klebanoff S, Kettle A, Rosen H, Winterbourn C, Nauseef W. Myeloperoxidase: a front-line defender against phagocytosed microorganisms. Journal of Leukocyte Biology. 2012;93(2):185-198. 
  4. Jayaseelan S, Ramaswamy D, Dharmaraj S. Pyocyanin: production, applications, challenges and new insights. World Journal of Microbiology and Biotechnology. 2013;30(4):1159-1168. 
  5. Kalakonda A, Jenkins B, John S. Physiology, Bilirubin [Internet]. 2022 [cited 28 September 2022]. Available from:
  6. Mishima Y, Nosaka N, Oi K, Gu Y, Arai H. Tracheobronchial aspergillosis presenting with black mucus plugs and tracheal ulcers. Clinical Case Reports. 2022;10(2). 
  7. Martínez-Girón R, Mosquera-Martínez J, Martínez-Torre S. Black-pigmented sputum. Journal of Cytology. 2013;30(4):274. 
  8. Don’t judge your mucus by its color - Harvard Health [Internet]. Harvard Health. 2022 [cited 28 September 2022]. Available from:
  9. Sinus Infections | [Internet]. 2022 [cited 28 September 2022]. Available from:
  10. What Are Bronchitis Symptoms? [Internet]. WebMD. 2022 [cited 28 September 2022]. Available from:
  11. Vaginal discharge When to see a doctor [Internet]. Mayo Clinic. 2022 [cited 28 September 2022]. Available from:
  12. Rosario D, Mendez M. Chronic Suppurative Otitis [Internet]. 2022 [cited 28 September 2022]. Available from:
  13. Nasal Congestion (Stuffy Nose): What It Is, Causes & Treatment [Internet]. Cleveland Clinic. 2022 [cited 28 September 2022]. Available from:
  14. Can a neti pot relieve your cold and sinus symptoms? [Internet]. Mayo Clinic. 2022 [cited 28 September 2022]. Available from:
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Mert Gurcan

Doctor of Medicine - MD, Medicine, Istanbul University-Cerrahpasa

Dr. Mert Gurcan is a Medical Doctor with extensive experience in conducting, directing, publishing, and presenting clinical research. He is passionate about making positive differences in the lives of individuals and their communities through research and promoting public and personal health solutions that help people live healthier and happier lives.
Having completed part of his medical school in the Charite Universitätsmedizin in Berlin, Dr. Gurcan graduated in 2020 from the Istanbul University - Cerrahpasa Medical Faculty with honors and many academic publications and he practiced for two years in Istanbul as both an emergency practicioner and an ENT trainee and is continuing his career in clinical medicine in the United Kingdom.

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