1. American College of Physicians https://acpinternist.org/archives/2011/01/sinusitis.htm
2. American Family Physician https://www.aafp.org/afp/2017/1015/p500.html
3. Canadian Family Physician https://www.cfp.ca/content/59/12/1275
4. Mayo Clinic, USA https://www.mayoclinic.org/diseases-conditions/chronic-sinusitis/symptoms-causes/syc-20351661
5. Medical News Today https://www.medicalnewstoday.com/articles/320569.php