It looks like you are using an older version of Internet Explorer which is not supported. We advise that you update your browser to the latest version of Microsoft Edge, or consider using other browsers such as Chrome, Firefox or Safari.


What are the sinuses?

The sinuses are a group of hollow (air-filled) cavities in our skulls.1

They are divided into four broad categories:2    

  • maxillary sinuses, the largest sinuses, in our cheekbones3     
  • frontal sinuses low in the centre of our foreheads     
  • ethmoid sinuses between our eyes    
  • sphenoid sinuses in the bones behind our noses1

Why do we have sinuses?

Experts do not completely agree on all the possible purposes sinuses have, but these may include:3

  • making our facial bones lighter     
  • improving our voice resonance    
  • absorbing some impact if we receive a hard blow to the head    
  • aiding our sense of smell.

There is, however, general agreement that:    

  • the sinuses humidify (increase the level of moisture in) the air we breathe in2,3    
  • soft pink tissue (called the mucosa or mucous membrane)4 lines the sinuses and produces a thin layer of mucus.5

In healthy sinuses, the mucosa is working well, producing a thin layer of mucus that captures foreign particles that are breathed in.2,3,6 The cilia (small hair-like structures in the mucosa) help to clear the foreign bodies captured by the mucus, using a ‘sweeping’ action to move them out.3 In this way, the sinuses effectively keep the upper airways free of dust, bacteria and other germs, stopping them from reaching the lungs. This helps to keep us healthy and free from infection.3,7


What is sinus congestion (a symptom of sinusitis)?

Sinusitis occurs when the mucous lining of the sinuses becomes inflamed (swollen) and starts to produce extra mucus, which is often thick.2,8 The inflammation and excess mucus block the sinuses8,13 and interfere with the functioning of the cilia.3 When your sinus drainage and mucus clearance are compromised, you are left feeling congested (blocked-up)8 and your risk of infection increases.5


Signs and symptoms of sinusitis

You are likely to experience some of the following:    

  • facial pain and pressure8,9    
  • nasal congestion or stuffiness9   
  • pus-like nasal discharge3    
  • pus-like mucus draining into the back of the throat (postnasal drip)3,9   
  • fever3,8,9   
  • reduced sense of smell8    
  • headache3    
  • tooth pain3,8    
  • earache3    
  • ear fullness and clicking9    
  • cough3,9    
  • sore throat3    
  • increased wheeze3 
  • foul breath3,9   
  • malaise (general feeling of discomfort, illness or unease)8

Children may experience increased irritability, vomiting and prolonged cough.3


What causes sinusitis?

Sinusitis can be caused by many different factors, including particulates (pollen, dust, dirt, fungal-spores),1,11 allergies,8,11 viral or bacterial infections,8,9,10 anatomical abnormalities3,8 and abnormalities of the immune system.3

The most common cause of sinusitis is a viral infection,8,9,10,11 although allergies are another common cause.2 Other cases of sinusitis may be caused by a bacterial infection, or may start as a viral infection and become a bacterial infection. Research suggests that if your sinusitis has lasted longer than 10 days, you may have a bacterial infection.12

Other factors like cigarette smoking, swimming, diving, high-altitude climbing, having diabetes or dental infections, and undergoing dental procedures can also increase your risk of developing sinusitis.8


What is the difference between acute and chronic sinusitis?

Acute sinusitis is likely to come on suddenly,9 with symptoms lasting for less than eight weeks in children and less than 12 weeks in adults.3 Acute sinusitis becomes chronic sinusitis when it lasts longer than eight to 12 weeks.3 Why some people develop chronic sinusitis and others don’t is not well understood, but some evidence suggests that allergies play a role.2

  1. Hoffmann M. Picture of the sinuses. Last updated: 2014. Available at: Last accessed May 2019.
  2. Helms S and Miller AL. Natural treatment of chronic rhinosinusitis. Altern Med Rev 2006; 11(3):196-207.
  3. Hallet R and Naguwa SM. Severe rhinosinusitis. Clin Rev Allergy Immunol 2003; 25:177-190.
  4. Robson K. What are sinuses? Available at: Last accessed May 2019.
  5. Knowles MR and Boucher RC. Mucus clearance as a primary innate defense mechanism for mammalian airways. J Clin Invest 2002 01 Mar; 109(5):571-577.
  6. Asthma and Allergy Foundation of America. Rhinitis (nasal allergies). Last updated: Oct 2015. Available at: Last accessed May 2019.
  7. Macchi A et al. Recurrent acute rhinosinusitis: a single blind clinical study of N-Acetylcysteine vs Ambroxol associated to corticosteroid therapy. Int J Immunopathol Pharmacol 2012; 25(1):207-217.
  8. Ah-See KW and Evans AS. Sinusitis and its management. BMJ 2007; 334:358-361.
  9. Lanza DC and Kennedy DW. Adult rhinosinusitis defined. Supplement to Otolaryngol Head Neck Surg 1997; 117(3.2):S1-S7.
  10. Scheid DC and Hamm RM. Acute bacterial rhinosinusitis in adults: part 1. Evaluation. Am Fam Physician; 70(9):1685-1692.
  11. Lau J et al. Diagnosis and treatment of acute bacterial rhinosinusitis: summary. In: Agency for Healthcare Research and Quality (US) 1999. Available at: Last accessed May 2019.
  12. Rosenfeld RM et al. Clinical practice guidelines (update): adult sinusitis. Otolaryngol Head Neck Surg 2015; 152(2S):S1-S39.
  13. BMJ Best Practice. Acute sinusitus. Last updated: 01 Mar 2019. Available at: accessed May 2019.