Phlegm can be different colors depending on its constituents. Chemicals, disease, the body’s cellular debris in response to invasion and other particulates in the mucus of the airways are major contributors to the color of phlegm. Phlegm color can tell you something about how serious your ailment is or if you need to contact a doctor to interpret your symptoms.
Your airways are lined with glandular cells that secrete mucus, a clear, slow-flowing liquid protein with properties that are antiseptic and resistant to disease. The thick mucus rides on another layer of clear watery fluid. Unless you cough up the mucus or blow it out your nose, microscopic hairs on cells lining the airways bring the mucus, and anything caught in it, out of the lungs or upper nasal passages.
Nasal and lung mucus, to be eliminated from the body, pool above the entrances to the trachea and esophagus. The body's reflex will be to cough the mucus up as phlegm when the mucus is close to the tracheal opening. Whatever mucus remains is swallowed into the esophagus for re-absorption by the small intestine or elimination from the body.
Some phlegm color may be due to the body’s own broken down cells or the dead invading organisms. Red blood cells and plasma from vascular tissue lining the airways brings oxygen and nutrients to the respiratory cells. White blood cells attack invaders and die and are swept up in the mucus toward the esophagus, to be reabsorbed or eliminated from the body.
When your body is attacked by viruses, bacteria, or other invading cellular organisms, the phlegm color usually changes from yellow to green as the infection becomes more severe. If the infection is slight, or if the infecting particles are small and dispersed in the mucus, viruses for example, phlegm will remain transparent because light will continue to pass through the mucus without obstruction. When your lungs are attacked by particulates such as smoke, dust, or industrial debris, the phlegm color can range from brown to black and large particles can be seen, sometimes without magnification. When phlegm is colored pink or red, it is sometimes a sign that the body cannot fight off disease and blood vessels are under attack.
Ancient doctors and alchemists believed that each phlegm color signified a different ailment. Today, it is understood that the color of phlegm can give you valuable information about the intensity of your body’s disturbance with respect to disease, chemical, and environmental pollutants. If there is a change in normal, usually clear phlegm for any length of time, especially if other symptoms persist, the advice of a physician is usually recommended so that he or she might look more closely at the microscopic appearance of your phlegm to identify your condition.