The vital role of mucus and phlegm

With cold and flu season upon us, it’s worth noting that as much as nobody likes to cough, it can actually be good for you. In order to better understand this, it is important to understand what mucus is, how it is different to phlegm, and the role that both play in our bodies, especially in relation to coughs.

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

Mucus is a useful material with important functions in the body. It acts as a thin, protective blanket preventing the tissue underneath from drying out. Without mucus, the mucosa will be exposed to elements from the outside world, which will cause it to dry out and crack. So mucus serves an important role to keep these tissues healthy. Mucus is also able to trap unwanted substances like bacteria and dust before it gets into our bodies. Furthermore, mucus contains elements of the immune system that kill any invaders it traps.


The respiratory tract is a mucus-making machine, producing over a litre of mucus a day. This ensures that the protective mucus blanket is constantly supplied with newly made mucus. Many cells lining the airways have long, tail-like hair called cilia, which beat 10-12 times per second. The mucus blanket rests on top of the cilia, which propel it forward like an escalator. Once mucus reaches the throat, it is swallowed, usually unnoticed, and recycled in the stomach. The normal amount of mucus produced daily is very effectively handled and cleared by the mucus escalator to prevent it from accumulating.


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


When the mucus escalator can’t keep up, the body deploys other strategies such as coughing. A cough that produces mucus is known as a chesty or wet cough. 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 ability of lungs to fight infection.


This is where mucolytics have a key role to play. Mucolytics are useful to alleviate coughing, mucus production and airway obstruction. They break the chemical bonds that hold mucus together in a sticky elastic gel. When the bonds are broken, the mucus becomes less sticky and thick, making it easier to move along the mucus escalator and cough up. This also makes it harder for germs to infect the mucus and cause chest infections.

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


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

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

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