Your sinuses are air-filled cavities in your facial bones that are lined with mucus-producing membranes. As mucus is produced, it leaves the sinus through a small opening and goes into your nasal cavity.
When the mucous membranes become inflamed, swelling blocks the opening and mucus is trapped in the sinus.
As the mucus accumulates, an infection called sinusitis develops. The fluids and swelling inside your sinuses cause a significant amount of pressure. As a result, you get a sinus headache.
You can also get a sinus headache from nasal congestion, whether it’s due to a cold, allergies, or a physical obstruction.
An infection that starts in your nose may spread into your sinuses. It’s also possible for nasal congestion to block the sinus opening, resulting in the buildup of mucus and sinus pressure.