The color of mucus may vary although it usually clear in color. Its if often mixed with saliva when passed out through the mouth (spitting or coughing).
Clear, thin and watery mucus (serous) or clear to white, thick mucus (mucoid) is often accepted as the normal color and may be seen in the early stages of an infection or other inflammatory conditions. Pink to red or rust colored mucus is a sign of blood within the mucus and is usually associated with a severe infection or inflammatory response.
Why is mucus green?
Green mucus is a result of dead neutrophils, a type of white blood cell active in infectious and inflammatory responses, within the sputum. When neutrophils die and burst (lysis), it releases a green pigment known as verdoperoxidase. This is an enzyme responsible for the perioxidase activity of pus.
Initially, in the acute stage of an infection or inflammation, the presence of live neutrophils causes the mucus to be yellow in color. Another type of white blood cell known as an eosinophil, which is often seen in allergy-related conditions like asthma, also causes mucus to be yellow in color. As the infection or inflammation becomes longer lasting (sub-acute or chronic), the lysis of neutrophils results in green mucus.
There is a common misconception that yellow to green mucus is associated specifically with bacterial infections. Neutrophil activity is seen in the presence of any invading pathogen, whether it is bacteria, viruses or fungi. Prolonged inflammatory responses, even if not due to infectious causes, will also result in green mucus.
Causes of Green Mucus
Mucus is often secreted in excess in certain conditions, especially in respiratory tract infections. It may originate from from the nose of mouth (catarrh) or from lower down the respiratory tract (sputum, phlegm). Rarely, it may emanate from the upper esophagus.
- Flu (infleunza)
- Hay fever
- Acute bronchitis
- COPD , particularly in chronic bronchitis
- Lung abscess
- Cystic fibrosis