ADVERTORIAL: What is mucus, how it is different to phlegm and what role do both play in our bodies?

The truth about mucus and phlegm and the vital role both play in your body

With cold and flu season upon us, it’s worth noting that although nobody likes a cough, it actually has positive attributes. In order to better understand this, it is important that we know what mucus is, how it is different to phlegm and the role that both play in our bodies, especially in relation to coughs.

What is mucus and what function does it serve?

Mucus is the slippery liquid made by our mucus membranes or mucosa.1Apg1 These membranes line the passageways in our bodies that come into contact with the outside environment. They include the nose, mouth, airways, digestive tract, the reproductive tract, the white part of the eye and the inside of the eyelids.1Apg1

Mucus is a useful material with important functions.1Apg1,2Apg1 It acts as a thin, protective blanket preventing the tissue underneath from drying out.2Bpg1 Without mucus, these areas will be exposed to elements from the outside world, which will cause them to dry out and crack.3Apg1

Mucus therefore plays an important role in keeping these tissues healthy.3Apg1 Mucus is also able to trap unwanted substances like bacteria and dust, preventing them from getting into our bodies.2Cpg1,3Apg1 Furthermore, mucus is part of the body's immune system and kills any invaders it traps.2Dpg13Apg1

The respiratory tract is a mucus-making machine, producing over a litre of mucus a day.3Bpg1 This ensures that the protective mucus blanket is constantly supplied with fresh mucus.4Apg2

Many cells lining the airways have long, tail-like hairs called cilia, which beat 10 to 12 times per second.4Bpg2 The mucus blanket rests on top of the cilia, which propel it forward like an escalator.5Apg208 Once mucus reaches the throat, it is swallowed, usually unnoticed, and recycled in the stomach.4Apg2,5Apg208

The normal amount of mucus produced daily is very effectively handled and cleared by the mucus escalator to prevent it from accumulating.5B+Cpg208

Phlegm: mucus accumulation

A bad cold or an allergy can throw the body’s mucus production into overdrive.2Epg2 This is the body’s way to flush away infection, irritants or allergens.4Cpg2

However, the mucus escalator may not be able to keep up with the increased volume of mucus, or may become inefficient due to the stickiness of the mucus.5Dpg208 As a result, large volumes of thick, sticky mucus accumulate in the airways. Mucus from the lungs is sometimes referred to as phlegm and is produced by the lower airways.6Apg2

A chesty cough

When the mucus escalator can’t keep up, the body deploys other strategies such as coughing.4Dpg2 A cough that produces mucus is known as a chesty or wet cough.7Apg30 Unlike a dry cough, a wet cough should be encouraged because it prevents mucus from pooling in the lungs, which can impair breathing and the lungs' ability to fight infection.7Apg30

Why mucolytics work best

This is where mucolytics have a key role to play. Mucolytics are useful to alleviate coughing, mucus production and airway obstruction.8Apg1181 They break the chemical bonds that hold mucus together in a sticky elastic gel.8Bpg1184 When the bonds are broken, the mucus becomes less sticky and thick, making it easier to move along the mucus escalator and cough up.9Apgs216,10Apg1

This also makes it harder for germs to infect the mucus and cause chest infections.10Apg1

N-Acetylcysteine (NAC) is the most commonly used mucolytic to loosen secretions from the airway.11Apg106 A scientific review has shown that NAC is effective for wet cough with good overall safety in adults and children older than two years.12Apg2 NAC is available from your local pharmacy as an effervescent tablet and is suitable for children and adults. The package insert of the product should however always be consulted before use.


Mucus plays an essential role in the maintenance of a healthy body and respiratory tract.1Apg1,2Apg1 Infections, irritants and allergies can stimulate mucus overproduction, causing large volumes of thick, sticky mucus to accumulate in the respiratory tract. 2Epg2,5Dpg208

A wet cough helps to remove mucus and should be encouraged, rather than suppressed.7Apg30 N-acetylcysteine (NAC) is a mucolytic that breaks the chemical bonds that hold mucus together, making it thinner, less sticky and easier to cough up.10Apgs1

1. Crampton L. Mucus in the human body: functions and health problems, 2017. [cited 2017 March 13]; Available from:
2. Watson S. The truth about mucus. WebMD® [online]. [cited 2017 March 09]; Available from:
3. Shmerling RH. Don’t judge mucus by its colour. Harvard Health Publications, Harvard Medical School, 2016. [cited 2017 March 13]; Available from:
4. King D. Health Check: what you need to know about mucus and phlegm. The Conversation, 2014. [cited 2017 March 09]; Available from:
5. Farzan S. Cough and sputum production. In: Clinical methods: The history, physical, and laboratory examinations, 3rd ed. Walker HK, Hall WD, Hurst JW, editors. Boston: Butterworths; 1990. Pg 207-210. [cited 2017 March 09]; Available from:
6. Vann MR. Everything you ever wondered about phlegm and mucus. New York: Everyday Health, Inc; [updated 2010 September 09; cited 2017 March 09]. Available from:
7. Van Schoor J. An approach to recommending cough mixtures in the pharmacy. S Afr Pharm J 2012;79(6):30-33.
8. Rogers DF. Mucoactive agents for airway mucus hypersecretory diseases. Resp Care 2007;52(9):1176-1197.
9. Rubin BK. The pharmacologic approach to airway clearance: mucoactive agents. Paed Resp Rev 2006;7S:S215-S219.
10. Payne J. Mucolytics., 2015. [cited 2017 Feb 22]; Available from:
11. Majima Y. Mucoactive medications and airway disease. Mini symposium: mucus. Paed Resp Rev 2002;3:104-109.
12. Chalumeau M, Duijvestijn YCM. Acetylcysteine and carbocysteine for acute upper and lower respiratory tract infections in paediatric patients without chronic broncho-pulmonary disease. Cochrane Database of Systematic Reviews 2013, Issue 5. Art. No.: CD003124. DOI: 10.1002/14651858.CD003124.pub4

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