The internal sinus wall, which is the same as the nasal airway, produces mucus composed of bacteria, dust, pollen, and other particles. This mucus makes the inhaled air very humid, which is then warmed by the blood vessels before entering the lungs.

Nasal congestion is caused by an increase of the blood flow to the nasal walls, which provokes a high production of mucus and inflammation. This is due to a virus, bacterial infection, or allergy.

If you have at least two of the following symptoms, you will rapidly develop sinusitis:
Sore throat, maxillary pain, bad breath, cough, leaking of mucus in the back of the throat, thick and greenish nasal mucus, nasal obstruction, facial sensitivity and pain, as well as headaches.