The Surgeons and Staff at California Sinus Centers recommend these sites:
Wikipedia: Sinusitis
https://en.wikipedia.org/wiki/Sinusitis
American Rhinologic Society: Conditions
https://sinushealth.com/conditions
American Academy of Otorhinolaryngology – Head & Neck Surgery: World Sinus Health Awareness Month
https://www.entnet.org/about-us/campaigns/world-sinus-health-awareness-month/