When you have sinusitis, the mucous membranes of your nose, sinuses and throat (upper respiratory tract) become inflamed. Swelling obstructs the sinus openings and prevents mucus from draining normally, causing facial pain and other sinusitis symptoms.

Blocked sinuses create a moist environment that makes it easier for infection to take hold. Sinuses that become infected and can't drain become pus filled, leading to signs and symptoms such as thick, yellow or greenish discharge and other symptoms of infection.

Acute sinusitis can be caused by:

  • Viral infection. Most cases of acute sinusitis are caused by the common cold.
  • Bacterial infection. When an upper respiratory tract infection persists longer than seven to 10 days, it's more likely to be caused by a bacterial infection than by a viral infection.
  • Fungal infection. You're at increased risk of a fungal infection if you have sinus abnormalities or a weakened immune system.

Some health conditions can increase your risk of getting a sinus infection that causes sinusitis, or can increase your risk of getting sinusitis that isn't caused by an underlying infection. These conditions include:

  • Allergies such as hay fever. Inflammation that occurs with allergies may block your sinuses.
  • Nasal polyps or tumors. These tissue growths may block the nasal passages or sinuses.
  • Deviated nasal septum. A crooked septum — the wall between the nostrils — may restrict or block sinus passages.
  • Tooth infection. A small number of cases of acute sinusitis are caused by an infected tooth.
  • Other medical conditions. The complications of cystic fibrosis, gastroesophageal reflux disease (GERD) or immune system disorders may result in blocked sinuses or an increased risk of infection.
Jul. 02, 2013