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Phlegm (; , ''phlégma'', "inflammation", " humour caused by heat") is mucus produced by the respiratory system, excluding that produced by the nasal passages. It often refers to respiratory mucus expelled by
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three phas ...
ing, otherwise known as
sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigation ...
. Phlegm, and mucus as a whole, is in essence a water-based gel consisting of glycoproteins, immunoglobulins, lipids and other substances. Its composition varies depending on
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
, genetics, and state of the immune system. Its color can vary from transparent to pale or dark yellow and green, from light to dark brown, and even to dark grey depending on the constituents. The body naturally produces about 1 quart (about 1 litre) of phlegm every day to capture and clear substances in the air and bacteria from the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passe ...
and throat.


Distinction between mucus and phlegm

Contrary to popular misconception and misuse, mucus and phlegm are not always the same.


Mucus

Mucus is a normal protective layering around the airway, eye, nasal turbinate, and
urogenital tract The genitourinary system, or urogenital system, are the organs of the reproductive system and the urinary system. These are grouped together because of their proximity to each other, their common embryological origin and the use of common pathwa ...
. Mucus is an adhesive viscoelastic gel produced in the airway by
submucosal glands Submucosal glands can refer to various racemose exocrine glands of the mucous type. These glands secrete mucus to facilitate the movement of particles along the body's various tubes, such as the throat and intestines. The mucosa is the lining of th ...
and
goblet cells Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their sec ...
and is principally water. It also contains high-molecular weight mucous glycoproteins that form linear polymers.


Phlegm

Phlegm is more related to disease than is mucus and can be troublesome for the individual to excrete from the body. Phlegm is a thick secretion in the airway during disease and inflammation. Phlegm usually contains mucus with virus, bacteria, other debris, and sloughed-off inflammatory cells. Once phlegm has been expectorated by a cough, it becomes
sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigation ...
.


Excessive phlegm creation

There are multiple factors that can contribute to an excess of phlegm in the throat or larynx. *Vocal abuse: Vocal abuse is the misuse or overuse of the voice in an unhealthy fashion such as clearing the throat, yelling, screaming, talking loudly, or singing incorrectly. ** Clearing the throat: Clearing the throat removes or loosens phlegm but the vocal cords hit together causing inflammation and therefore more phlegm. ** Yelling/screaming: Yelling and screaming both cause the vocal cords to hit against each other causing inflammation and phlegm. ** Nodules: Excessive yelling, screaming, and incorrect singing as well as other vocal abusive habits can cause vocal fold nodules. * Smoking: Smoke is hot, dry, polluted air which dries out the vocal cords. With each breath in of smoke, the larynx is polluted with toxins that inhibit it from rehydrating for about 3 hours. The vocal cords need a fair amount of lubrication and swell from inflammation when they do not have enough of it. When the vocal folds swell and are inflamed, phlegm is often created to attempt to ease the dryness. **Experiment on smoking correlations: In 2002, an experiment was done and published by the
American College of Chest Physicians The American College of Chest Physicians (CHEST) is a medical association in the United States consisting of physicians and non-physician specialists in the field of chest medicine, which includes pulmonology, critical care medicine, and sleep med ...
to find if there was a correlation of smokers with coughing and phlegm. In the study, 117 participants were studied, a mix of current smokers, ex-smokers, non-smokers, and a positive control of participants with a disease, COPD (
Chronic Obstructive Pulmonary Disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce m ...
). At the end of the experiment, experimenters found that there was a high correlation between phlegm and cough with smoking of 0.49 (p < 0.001.) * Illness: During illness like the flu,
cold Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
, and pneumonia, phlegm becomes more excessive as an attempt to get rid of the bacteria or viral particles within the body. A major illness associated with excess phlegm is
acute bronchitis Acute bronchitis, also known as a chest cold, is short-term bronchitis – inflammation of the bronchi (large and medium-sized airways) of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortn ...
. A major symptom of acute bronchitis is an excess amount of phlegm and is usually caused by a viral infection, and only bacterial infections, which are rare, are to be treated with an antibiotic. * Hay fever, asthma: In hay fever and asthma, inner lining in
bronchioles The bronchioles or bronchioli (pronounced ''bron-kee-oh-lee'') are the smaller branches of the bronchial airways in the lower respiratory tract. They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start o ...
become inflamed and create an excess amount of phlegm that can clog up air pathways. *
Air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different type ...
: In studies of children, air pollutants have been found to increase phlegm by drying out and irritating parts of the throat.


Removing phlegm

Excessive phlegm creation can be troublesome. There are basically two ways to get rid of excess phlegm: swallowing or spitting. Phlegm naturally drains down into the back of the throat and can be swallowed without imposing health risks. Once in the
stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
, the
acids In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
and
digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compon ...
will remove the phlegm and get rid of the germs in it. In some cultures, swallowing phlegm is considered a social taboo, being described as disgusting or unhygienic. One Igbo
adage An adage (; Latin: adagium) is a memorable and usually philosophical aphorism that communicates an important truth derived from experience, custom, or both, and that many people consider true and credible because of its longeval tradition, i.e. ...
, for example, uses the swallowing of phlegm as a
metaphor A metaphor is a figure of speech that, for rhetorical effect, directly refers to one thing by mentioning another. It may provide (or obscure) clarity or identify hidden similarities between two different ideas. Metaphors are often compared wit ...
for
wrongdoing A wrong (from Old English – 'crooked') is an act that is illegal or immoral. Legal wrongs are usually quite clearly defined in the law of a state and/or jurisdiction. They can be divided into civil wrongs and crimes (or ''criminal offenses'') ...
. Also, due to the social image of spitting (the alternative of swallowing) in some communities, females were shown to be more likely to swallow phlegm and less likely to report experiencing it. The alternative to swallowing would be throat-clearing. To do this, the mouth should be closed and air should be
inhaled Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
hard into the nose. Inhaling forcefully through the nose will pull excess phlegm and nasal mucus down into the throat, where muscles in the throat and
tongue The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste b ...
can prepare to eject it. Once this is done, a U-shape should be formed with the tongue, while simultaneously forcing air and
saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...
forward with the muscles at the back of the throat. At this point, the phlegm will be in the mouth and is now ready to be spat out as
sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigation ...
.


Colors of phlegm

Phlegm can exist in different colors. The color could provide important clues about a person's health. * Yellow or green: Indicates an infection often by a virus or bacteria. The color is caused by an enzyme produced by the white blood cells combating the infection. * Clear: Indicates
allergies Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermat ...
. Mucus membranes produce
histamines Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered i ...
and make more phlegm. * Red: Indicates dry air. A
nasal spray Nasal sprays are used to deliver medications locally in the nasal cavities or systemically. They are used locally for conditions such as nasal congestion and allergic rhinitis. In some situations, the nasal delivery route is preferred for syst ...
can be used to alleviate symptoms of a dry nose and throat. It can also occur due to blood (such as if the person had or has a bleeding nose, or a lung malignancy).


Phlegm and humourism

Humourism Humorism, the humoral theory, or humoralism, was a system of medicine detailing a supposed makeup and workings of the human body, adopted by Ancient Greek and Roman physicians and philosophers. Humorism began to fall out of favor in the 1850 ...
is an ancient theory that the human body is filled with four basic substances, called the ''four humours'', which are held in balance when a person is healthy. It is closely related to the ancient theory of the four elements and states that all diseases and disabilities result from an excess or deficit in black bile, yellow bile, phlegm, and blood. Hippocrates, an ancient Greek medical doctor, is credited for this theory, about 400 BC. It influenced medical thinking for more than 2,000 years, until finally discredited in the 1800s. Phlegm was thought to be associated with
apathetic Apathy is a lack of feeling, emotion, interest, or concern about something. It is a state of indifference, or the suppression of emotions such as concern, excitement, motivation, or passion. An apathetic individual has an absence of interes ...
behaviour; this old belief is preserved in the word "
phlegmatic The four temperament theory is a proto-psychological theory which suggests that there are four fundamental personality types: sanguine, choleric, melancholic, and phlegmatic. Most formulations include the possibility of mixtures among the types w ...
". This adjective always refers to behaviour, and is pronounced differently, giving full weight to the "g": not /ˈflɛmatɪk/ but /flɛgˈmatɪk/. To have "phlegm" traditionally meant to have stamina and to be unswayed by emotion. Sir
William Osler Sir William Osler, 1st Baronet, (; July 12, 1849 – December 29, 1919) was a Canadian physician and one of the "Big Four" founding professors of Johns Hopkins Hospital. Osler created the first residency program for specialty training of phy ...
’s 188
Aequanimitas
discusses the imperturbability or calmness in a storm required of physicians. "'Imperturbability means coolness and presence of mind under all circumstances, calmness amid storm, clearness of judgment in moments of grave peril, immobility, impassiveness, or, to use an old and expressive word, phlegm."'' This was his farewell speech at the University of Pennsylvania in 1889 before becoming Physician-in-Chief at the recently founded
Johns Hopkins Hospital The Johns Hopkins Hospital (JHH) is the teaching hospital and biomedical research facility of the Johns Hopkins School of Medicine, located in Baltimore, Maryland, U.S. It was founded in 1889 using money from a bequest of over $7 million (1873 mo ...
in
Baltimore, Maryland Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was ...
. This is fro
''"Celebrating the Contributions of William Osler"''
in th
Alan Mason Chesney Medical Archives
of th
Johns Hopkins Medical Institutions
"'' The phlegm of Humourism is far from the same thing as phlegm as it is defined today. Nobel laureate
Charles Richet Charles Robert Richet (25 August 1850 – 4 December 1935) was a French physiologist at the Collège de France known for his pioneering work in immunology. In 1913, he won the Nobel Prize in Physiology or Medicine "in recognition of his work on ...
MD, when describing humorism's "phlegm or pituitary secretion" in 1910 asked rhetorically, "this strange liquid, which is the cause of tumours, of chlorosis, of rheumatism, and cacochymia - where is it? Who will ever see it? Who has ever seen it? What can we say of this fanciful classification of humours into four groups, of which two are absolutely imaginary?"Charles Richet, MD, Professor of Physiology, University of Paris. Ancient Humorism and Modern Humorism. Delivered at the International Congress of Physiology held in Vienna, September 27th to 30th 1910, as reported on page 921 of the British Medical Journal of October 1, 1910:


Illnesses related to phlegm

Phlegm may be a carrier of larvae of
intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and inf ...
s (see hookworm). Bloody sputum can be a symptom of serious disease (such as tuberculosis), but can also be a relatively benign symptom of a minor disease (such as
bronchitis Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. S ...
). In the latter case, the sputum is normally lightly streaked with blood. Coughing up any significant quantity of blood is always a serious medical condition, and any person who experiences this should seek medical attention. Apophlegmatisms, in pre-modern medicine, were medications chewed in order to draw away phlegm and humours.


References

{{Authority control Body fluids Symptoms and signs: Respiratory system