The eight sinuses located in the air-filled spaces of your facial bones are lined with mucus-producing membranes. The mucus leaves the sinuses through a small opening and drains into your nose, where it moistens and warms the air you inhale.

Sinus membranes block the opening when they become inflamed and swollen. As a result, mucus accumulates inside the sinus and an infection called sinusitis develops.

The top causes of sinusitis are:


Seasonal and year-round allergies such as hay fever frequently cause nasal congestion, which in turn blocks the sinus opening and causes sinusitis. Common allergens likely to cause sinusitis include mold, dust mites, and pollen from grasses and trees.

Viral infection

Sinusitis is usually caused by the same virus that’s responsible for the common cold. It’s unusual for bacteria to cause sinusitis, but you may develop a bacterial infection when your sinusitis persists. In rare cases, sinusitis begins due to a fungal infection.

Chronic inflammation

You have chronic sinusitis when your symptoms last for 12 weeks or longer without relief. This type of sinusitis is caused by ongoing inflammation without an active infection.