Cough

Why do we cough? Types of coughs and causes of coughing.

What are coughs?

A cough is a sudden expulsion of air from the passages of the upper respiratory tract (larynx, trachea, bronchi), sometimes also known as the upper airways.

Coughing serves the purpose of clearing these large tubes of mucus, bugs and foreign particles.

During a cough, the larynx (commonly known as the voice-box) is closed momentarily by the epiglottis. This is followed, almost simultaneously, by the contraction of muscles in the abdomen and chest, which builds up pressure within the upper airways.

When the epiglottis relaxes again, the larynx opens and a short burst of approximately 1.5 litres of air from our lungs is released through the upper airways giving rise to the characteristic coughing sound.

This blast of air has been measured at speeds of up to 50mph, pushing unwanted material out of the upper airways and also releasing up to 3,000 tiny droplets of saliva.

Coughs are something we are familiar with and we use this mechanism without thinking to clear a bit of ‘mucus’ at the back of our throat before speaking – these may be termed ‘everyday coughs’.

However, sometimes, coughs are not controllable, coming in spasms. Most often, these are associated with viral infections such as colds or flu, with these infections causing inflammation which in turn trigger the cough reflex.

The cough reflex

Coughing is one of the body’s protective mechanisms. It usually indicates that there is something in the upper airways that shouldn’t be there. This protection afforded by coughing is maintained by the cough reflex.

The lining of our respiratory tract, from the back of our throat to the depths of our lungs, is richly supplied by nerve endings. When these are irritated, a nerve signal goes to the cough centre of the brain – this has the job of coordinating a series of signals to the epiglottis, trachea, muscles in the chest and abdomen, leading to a cough.

Coughs help us stay healthy by keeping unwanted material out of our lungs, leaving them clear to do the work of getting oxygen into our bodies. This job is done by:

• Expelling unwanted organisms from the upper airways. Coughs help to keep the lung tissue clear of bugs and infective organisms
• Coughs also help protect us when food or other objects enter the upper airways by mistake

Dry cough vs chesty cough

Coughs are most commonly caused by viral infections, typically those giving rise to colds and flu. However, not everyone with a cold or flu experiences a cough.

Certain types and strains of viruses cause coughs more often than others – in a way, these are better in what they do as coughing helps to spread the disease from one person to another, helping to ensure that the particular virus is successful.

Viruses can produce dry coughs or chesty coughs:

• A dry cough  produces little or no mucus (phlegm) and it is because of this that it is sometimes also referred to as a non-productive cough. When mild, a dry cough may also be described as a tickly cough. Dry coughs arise because inflammation of the lining of the upper airways irritates nerve endings, triggering the cough reflex.
• Chesty coughs are also known as productive coughs as coughing brings up mucus, catarrh or phlegm. Typically, these infections are lower down in the respiratory tract and lead to an overproduction of mucus. Nerve endings are irritated and the cough reflex is triggered with the aim of clearing out the tubes of the respiratory system, making it easier for air to enter the lungs.

Other causes of coughing

Other reasons or conditions giving rise to coughs include:

• Air pollution or entering a smoky atmosphere
• Asthma
• A chest infection (pneumonia), better described as infection of the deeper tissues of the respiratory tract
• Other infections of the lungs (eg. whooping cough, croup)
• Diseases of the lungs such as chronic obstructive pulmonary disease (COPD)
• A blood clot in the lungs
• Heart problems, especially heart failure
• Certain types of prescribed medicines such as the class of drugs known as ACE inhibitors (Acetyl-Choline Esterase inhibitors)
• Nervousness

See your doctor if you are suffering from one of the conditions above and experiencing an unexplained cough or a cough which does not improve within 3 weeks. In addition, you must seek medical attention urgently if you are coughing up blood.

Smoker’s cough

Smoking introduces irritants into the respiratory tract. The lining of the airways become covered in carbon particles inhaled when smoking, leading to an increase in production of mucus by the lining of the lungs.

In addition to all this, the body’s immune system brings white blood cells to the surface of the lungs in order to clean up the carbon particles. These cells mix with mucus and irritate the lining of the lungs further, triggering the cough reflex.

It is for this reason that people who smoke tend to cough more – giving rise to what we know as the smoker’s cough, bringing up large quantities of mucus, some of which can be thick or discoloured.

Further reading:
Chesty cough
Dry, tickly cough