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Most of us will recognise the early signs of a cold: the stuffy, runny nose caused by the swelling of tissues lining the nostrils, or the sore throat triggered by excess mucus production.1,2 Another common symptom, cough, often only appears a few days after the initial infection.2,3

Cough is a protective reflex – the body’s natural defence mechanism for clearing harmful content from the airways.4 The body creates a thin layer of mucus around debris in our airways and nasal passages and then uses coughing and the tiny movements of hair-like structures (called cilia) to expel these foreign bodies. The aim is to keep them out of our lungs.5  

Phlegm is a form of mucus produced by the lower airways, rather than by the nose and sinuses. It is the mucus you ‘cough up’ when you have a wet (or productive) cough.4,5,6  Understanding the difference between a productive and non-productive cough can be helpful when deciding on treatment.

If your cough is making you feel phlegmy and congested, this is usually a sign of increased mucus production due to infection. If no mucus is present, your cough is dry (or non-productive) and is probably caused by airway irritation or inflammation.4,6,7 Over time, a dry cough can evolve into a wet cough if the airways become irritated enough to trigger excess phlegm production.6  


The colour of phlegm

The colour of phlegm varies and is determined by different factors.8 Phlegm naturally comes in a range of shades from white to mustard-yellow, to different shades of green.8 Under normal conditions, when we are not sick, mucus in the airways is clear or white and translucent, and only contains a small number of microscopic particles.5

When we have a cold, more mucus is produced and it may be thicker, more opaque and a different colour: off-white, yellowish or greenish.5 This is because white blood cells, which are produced by the body to defend us against foreign materials and infections, are carried in phlegm.8 Some white blood cells contain a green protein, so the more of them that are present in the phlegm, the greener it will appear.8 


When to see your doctor

You should speak to your doctor if:7

  • your cough lasts for more than three weeks    
  • your cough is severe or getting worse     
  • you are coughing up blood     
  • you are experiencing shortness of breath, breathing difficulties or chest pain     
  • you are worried about other symptoms, such as:   

         –    unexplained weight loss   

         –    a persistent change in your voice     

         –    lumps or swellings in your neck. 


You should also speak to a doctor if your child has a cough alongside breathing difficulties, vomiting or a high fever of more than 37.8°C.9

A change in the colour of your phlegm is an indication that you might have some type of infection.10 However, it is important to understand that coughing up yellowish or greenish phlegm does not necessarily mean that you have a bacterial infection and need antibiotics.8,10 Phlegm can also be produced by some viral airway infections.10 Colds, flu, and other viruses cannot be treated with antibiotics.11

Various over-the-counter medications can be used to treat a cough. Some medications may help to relieve a cough and sinus congestion at the same time.

  1. Medline Plus. Stuffy or runny nose - adult. Available at: Last accessed Dec 2017.
  2. Blaiss MS et al. Consumer attitudes on cough and cold: US (ACHOO) survey results. Curr Med Res Opin 2015; 31:1527-1538.
  3. Janson C et al. Determinants of cough in young adults participating in the European Community respiratory health survey.Eur Respir J 2001; 18:647-654.
  4. Begic E et al. Productive cough in children and adolescents - view from primary health care system. Med Arch 2017; 71:66-68.
  5. Farzan S. Cough and sputum production. In: Walker HK et al. Clinical methods: the history, physical, and laboratory examinations.3rd edition. 1990; Chapter 38:207- 210.
  6. Alsubaie H et al. Clinical practice guidelines: approach to cough in children. Int J Ped Adol Med 2015; 2:38-43.
  7. NHS Choices. Cough. Available at: Last accessed Sep 2017.
  8. Public Health England. Green phlegm and snot ‘not always a sign of an infection needing antibiotics’. Available at: Last accessed 2017.
  9. American College of Chest Physicians. Patient information for parents of a child with a cough’. Available at: Education-Resources/~/~/media/EB930B8710664EFE861C97AF0D9EFAD1.ashx.Last accessed Feb 2018.
  10. Altiner A et al. Sputum colour for diagnosis of a bacterial infection in patients with acute cough. Scandinavian J Primary Healthcare 2009; 27:70-73. 11. CDC. Antibiotics aren’t always the answer. Available at: Last accessed Dec 2017.
  11. CDC. Antibiotics aren’t always the answer. Available at: Last accessed Dec 2017