Sinuses are air-filled cavities located behind your cheekbones and forehead. They are connected to your nose by small channels called ostia.

The primary function of the sinuses is unknown, but they may help to moisten, warm, and filter the air you breathe. Additionally, the sinuses give your face its shape and contribute to your voice.

There are four main types of sinuses: frontal, ethmoid, sphenoid, and maxillary. The frontal sinuses are located in your brow bone. The ethmoid sinuses are located between your eyes.

The sphenoid sinuses are behind your ethmoid sinuses and behind your nose. The maxillary sinuses are located under your eyes.

Healthy sinuses are important for the proper drainage of mucus. When the sinuses become blocked, mucus can build up and lead to infection.

Sinus infections (sinusitis) are common and can be caused by a virus, bacteria, or allergies. Symptoms of a sinus infection include a stuffy or runny nose, pain in the sinuses, fever, and headaches.

If you think you have a sinus infection, see your doctor. Treatment may include antibiotics, decongestants, or antihistamines. Some people may also need surgery to open the blocked channels.

Sinusitis is one of the most common conditions in the United States. It is estimated that 37 million people are affected by sinusitis each year. Sinusitis is more common in women, children, and people with allergies.