Paranasal Sinuses

What are the paranasal sinuses?

Your paranasal sinuses are four paired, air-filled spaces (cavities) inside the bones in your face. Most of us know them as just our “sinuses.” Technically speaking, “sinus” is a broad medical term that may refer to different air-filled cavities inside a bone or another type of tissue, like a blood vessel. For example, there are sinuses in your brain and heart.

But when most of us think about our sinuses, we mean the paranasal sinuses — the ones near (“para”) the nose (“nasal”). You likely don’t notice them until you have a cold, infection or allergies that are “acting up” and causing pressure in your face or a stuffy nose. Then, they’re impossible to ignore.

What do the paranasal sinuses do?

Your paranasal sinuses are more than a source of irritation when you’re sick. Although experts are still learning about all they do, some jobs your paranasal sinuses help with include:

• Helping fight infection. Your sinuses make mucus that drains into your nasal cavity and nose. The drainage gets rid of germs that may otherwise make you sick.
• Adding moisture and heat to the air you inhale. Your sinuses act as your body’s own built-in humidifier. They transform dry, cold air into air that’s warmer, wetter and healthier for your airways and lungs.
• Reducing the weight of your skull. These lightweight cavities counter the heaviness of bones that make up your skull.
• Absorbing the impact of head injuries. Paranasal sinuses serve as “crumple zones” or “crash zones” that absorb some of the force during head trauma. By absorbing some of the hit, they protect crucial structures, like your brain, from direct impact.
• Influencing how your voice sounds. Your sinuses act as resonators that help give your voice its uniqueness. When you speak, sound waves bounce off your paranasal sinus cavity walls. This makes your voice sound louder, warmer and more layered than it would otherwise.

Where are my paranasal sinuses located?

There are four paranasal sinus cavities. They’re paired, so you have one on the left side of your face and one on the right side. Each is named after the facial bone where it’s located. Together, they form a mucus drainage system that empties into your nasal cavity, the air-filled space behind your nose.

From top to bottom, your paranasal sinuses include:

• Frontal sinus: Your frontal sinuses are in your frontal bone (forehead area), above your eyebrows. They’re triangle-shaped but rarely symmetrical. The average frontal sinus in an adult is big enough to hold about 4 to 7 milliliters (mL) of air.
• Sphenoid sinus: Your sphenoid sinuses are inside your sphenoid bone, behind your eyes. Of all your sinuses, it’s the one deepest inside your head. They vary greatly in size depending on age, sex and ethnicity.
• Ethmoid sinus: Your ethmoid sinuses are between your eyes, behind the bridge of your nose. Unlike your other sinuses, each ethmoid sinus cavity consists of many tiny cavities (or pockets) called air cells. Your ethmoid sinuses hold between 2 to 3 mL of air.
• Maxillary sinus: Your maxillary sinuses are in your maxillary bone, the bone that makes up your upper jaw. They’re symmetrical, pyramid-like cavities, located beneath your eyes, on either side of your nose. Your maxillary sinuses are the largest paranasal sinuses and the most common site for a sinus infection to start. They hold between 15 to 20 mL of air.

Your sinuses drain into multiple passages that lead to your nasal cavity. A key one to know about is the ostiomeatal complex. It’s a pathway that includes many parts. It drains your frontal, ethmoid and maxillary sinuses. Blockages in this area make you particularly susceptible to inflammation (swelling) and infection.

What are conditions and disorders that affect my paranasal sinuses?

Most sinus conditions are related to inflammation in your sinuses, allergies or an infection. Abnormal growths sometimes form in the paranasal sinuses. They’re usually benign (noncancerous), but they can be precancerous or cancerous, as well.

Common conditions include:

• Sinus infection (sinusitis): Inflammation in the tissue lining your sinuses. Acute sinusitis typically involves having symptoms that last up to 10 days. With chronic sinusitis, symptoms last beyond 12 weeks. The most common causes are bacteria and viruses. With fungal sinusitis, a fungus causes the inflammation.
• Common cold: An upper respiratory infection in your sinuses, throat and windpipe. There are over 200 different viruses that can cause a cold, but the most common cause is rhinovirus.
• Nasal and paranasal tumors: Benign and cancerous growths that may form in your nose or sinuses. The most common benign tumors are nasal polyps. The most common cancers that affect your paranasal sinuses are squamous cell carcinoma (SCC) and adenocarcinoma.
• Silent sinus syndrome: A rare health condition where a blockage in your maxillary sinuses causes them to sink. As a result, your eyes may appear sunken.
• Dental infections: Only a thin bone separates your maxillary sinuses from the teeth in your maxillary bone (upper jaw). This makes it easy for dental infections to spread there.

Common signs or symptoms of a paranasal sinus condition

Signs and symptoms of simple, uncomplicated sinus conditions include (but are not limited to):

• Sinus pressure.
• Runny nose.
• Discolored drainage.
• Postnasal drip.
• Stuffy nose.
• Reduced sense of smell (hyposmia).

The aches, pains and pressure often correspond with where the inflammation is in your sinuses:

• Frontal sinus: Pain in your forehead.
• Sphenoid sinus: Pain behind your eyes or in your ears.
• Ethmoid sinus: Pain in the bridge of your nose.
• Maxillary sinus: Pain in your cheekbones or in your upper teeth.

Common tests to check the health of the paranasal sinuses

Healthcare providers can usually diagnose common causes or paranasal sinus issues with a physical exam and by considering your signs and symptoms. In some cases, your provider may perform an imaging procedure.

Nasal endoscopy may be an option if your provider needs to take a closer look at your sinuses or nasal passages and potentially take a sinus culture. For this test, your provider inserts a thin, flexible tube with a camera on the end into your nose. It records video of your sinuses that your provider can see on screen.

What are common treatments for paranasal sinus conditions?

Often, symptoms of common conditions, like sinusitis, are mild and go away on their own. But you may need medicines, like pain relievers to help with symptoms. Your provider can prescribe medications, like antibiotics, for bacterial infections.

Common treatments that can help manage symptoms include:

• Nonsteroidal anti-inflammatory drugs.
• Nasal decongestants.
• Nasal irrigation.
• Corticosteroids.

You may need sinus surgery for several reasons, including:

• If a sinus issue becomes chronic (long-lasting).
• If there’s a lesion (atypical tissue) in your sinuses.
• If a sinus infection becomes serious or spreads to your eye or brain.

How can I keep my paranasal sinuses healthy?

Avoiding viral infections (which can lead to bacterial infections) and managing your allergies is key. You can:

• Wash your hands regularly or use hand sanitizer to get rid of germs.
• Avoid things you’re allergic to (pollen, dust, mold, pet dander).
• Eat healthy food and get regular exercise and plenty of sleep.
• Avoid smoking or being around secondhand smoke.
• Clean surfaces you touch a lot.
• Use a humidifier in your home.

A note from Cleveland Clinic

Most of us don’t give our sinuses a second thought — until we’re sick and experiencing symptoms of a head cold or an infection that won’t let up. But your sinuses aren’t just sites of irritation. They’re immune system helpers that drain germs from your body. You can protect them by steering clear of allergens that may irritate them. Keep them free of infection by taking steps to keep from getting sick.