Catching the flu is never pleasant. Not only do we have a fever, headaches and achy muscles, we also often experience a bothersome cough ⁽¹⁾.

Let’s take a look at exactly why we cough when we have the flu and when our cough could indicate our illness is getting worse.

Why we cough when we have the flu

Coughing has a very important purpose when we have the flu. Coughing isn’t simply our body's way of clearing our airways of irritants such as dust or smoke ⁽²⁾; it’s also part of the defence system that protects our bodies from disease. Coughing helps us expels mucus, microbes and foreign particles from our airways, protecting our lungs from infection and inflammation ⁽³⁾.

When we cough we begin by gasping, which draws air deep into our lungs. Next, a lid shuts over our windpipe before the muscles in our chest, diaphragm and abdomen tighten. With the lid over our windpipe shut tight, air can't escape. Tremendous pressure builds up in our airways. Eventually, the lid over our windpipe swings open and air rushes out at a tremendous speed, making the noise we call a cough ⁽³⁾.

Our coughs can be productive or dry ⁽⁴⁾. Productive coughs produce phlegm or mucus that comes up from the lungs or drains down the back of the throat. Coughs producing mucus are clearing mucus from the lungs and should not be suppressed.

Dry (non-productive) coughs do not produce phlegm or mucus, and are usually our airway’s reaction to an irritant or to asthma ⁽⁴⁾. A cough associated with flu is usually dry ⁽⁵⁾.

While most other flu symptoms clear up within a week, the cough can be severe and may last two or more weeks ⁽⁶⁾.

When a cough gets worse

A cough that starts out dry but then gets worse and begins to produce a yellow-grey mucus is not normal. It may signal we have a flu-related complication such as bronchitis ⁽⁷⁾.

One of the more common complications of the flu, bronchitis occurs when we get a bacterial infection on top of the infection from the flu virus ⁽⁸⁾ causing our airways to produce more mucus than usual ⁽⁹⁾. Our coughing is simply our body trying to shift this extra mucus.

Bronchitis may, in turn, lead to pneumonia, which occurs when our bronchitis spreads further into our lungs ⁽¹⁰⁾. Around 1 in 20 cases of bronchitis lead to pneumonia.

The symptoms of pneumonia can develop suddenly over 24 to 48 hours, or they may come on more slowly over several days. While a cough is also a symptom of pneumonia, with pneumonia it may be dry, or produce thick yellow, green, brown or blood-stained mucus ⁽¹¹⁾.

Treating a cough

Most coughs go away on their own within three weeks ⁽¹²⁾. In the meantime, we should rest and drink plenty of fluids and hot lemon with honey. Hot lemon with honey has a similar effect as cough medicines ⁽¹²⁾. Cough syrups and lozenges can help reduce the coughing, but they won’t get rid of it altogether ⁽¹²⁾.

We should, however, seek medical advice if our cough lasts for more than three weeks, is particularly severe or is getting worse, or if we are short of breath or experiencing breathing difficulties or chest pain ⁽¹³⁾.

References
(1) https://ecdc.europa.eu/en/seasonal-influenza/facts/questions-and-answers-seasonal-influenza
(2) https://www.nhsinform.scot/illnesses-and-conditions/lungs-and-airways/cough
(3) https://www.health.harvard.edu/staying-healthy/that-nagging-cough
(4) https://my.clevelandclinic.org/health/diseases/16901-cough--dry-coughs
(5) https://ecdc.europa.eu/en/seasonal-influenza/facts/factsheet
(6) http://www.who.int/mediacentre/factsheets/fs211/en/
(7) https://www.nhsinform.scot/illnesses-and-conditions/lungs-and-airways/bronchitis
(8) https://ecdc.europa.eu/en/seasonal-influenza/facts/questions-and-answers-seasonal-influenza
(9) http://www.nhs.uk/conditions/Bronchitis/Pages/Introduction.aspx
(10) http://www.nhs.uk/conditions/Bronchitis/Pages/Introduction.aspx
(11) https://www.nhsinform.scot/illnesses-and-conditions/lungs-and-airways/pneumonia
(12) https://www.nhs.uk/conditions/cough/
(13) https://www.nhsinform.scot/illnesses-and-conditions/lungs-and-airways/cough