What are the Sinus Cavities?

Mary McMahon
Mary McMahon

The sinus cavities, also known as the paranasal sinuses, are hollows in the bones of the face which are designed to serve a number of important functions. Humans and many other animals including birds have sinuses. These cavities are only visible on X-rays, and in fact these cavities are unique, and they have been used like fingerprints in forensic examinations. The term “sinus” is actually Latin for “cavity,” making “sinus cavities” a rather redundant term, although many people are unaware of this.

A cross section of the head, including the sinuses.
A cross section of the head, including the sinuses.

There are four sets of sinuses in the skull. The ethmoid sinuses are located between the eyes, while the sphenoid sinuses are behind the eyes. In the upper jaw, underneath the eyes, one can find the maxillary sinuses, and the frontal sinuses are above the nose. Each cavity is lined with a mucus membrane and numerous cilia, tiny hairs which move, forcing the contents of the sinuses to move through the cavity and drain through the nose.

Sinus radiographs show the sinus cavities and possible problems or infections.
Sinus radiographs show the sinus cavities and possible problems or infections.

One of the key functions of the sinus cavities is to drain mucus. Mucus is used to trap harmful substances which could otherwise penetrate the body, and it is generated by the body all the time. The sinuses facilitate collection and drainage of mucus so that it cannot accumulate and cause the development of an infection. This reduces the risk of infection for the body as bacteria and viruses are caught in the mucus, and it can also trap potential allergens as well.

These cavities also filter and warm the air inhaled by the body, and they act to lighten the skull. If the sinus cavities were filled in with bone, the skull would be extremely heavy and dense, which would make it hard to move. The sinuses also add resonance to the voice, and help to protect the skull in the event of an impact to the face.

Sinuses can develop problems. The most common problem occurs when they become filled with mucus and are unable to drain, leading to sinusitis, in which an inflammation of the sinus cavities occurs. The failure to drain may cause pain, and it leaves people with a feeling of heaviness and fatigue. Chronic sinusitis can be extremely irritating, and in some cases a surgical technique may be used to enlarge the sinuses and their drainage outlets to reduce the buildup of mucus and fluid. Cancers can also develop in the sinuses, with the potential to metastasize to other areas of the body.

If sinuses do not drain, it can lead to sinusitis, an inflammation of the sinus cavities.
If sinuses do not drain, it can lead to sinusitis, an inflammation of the sinus cavities.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@sinbad - I have not used a neti pot but my husband uses one year around.

I think I will try to use a neti pot as soon as I have any signs of a sinus infection, you know that stuffiness more than normal with the added bonus of pressure on your nose, and that headache that seems to be at the sides of your forehead rather than the center of your forehead. Sinus infections are no fun!

Oh one other thing I have noticed when I have a sinus infection coming on, the symptoms worsen if I am bending over, lying down, etc than if I am upright. Has anyone else noticed this?


I used to never have sinus infections but now I have them every year! I blame it on my college boyfriend who used to get them yearly.

One of the things I do in addition to prescription medications to treat a sinus infection is use a neti pot. It looks just as it sounds. It is a little mini teapot (mine is plastic) and you mix saline with warm water and put it in the neti pot.

The next step is the interesting step. You take the end of the pot (where the water will come out) and put it in your nostril. This is why it is important not to put water that is too hot in the neti pot!

Next, you tilt your head as instructed in the neti pot instructions and start pouring the water into your nose. If you have your head tilted just the right way the water will come out your other nostril!

I use the neti pot in addition to medicine because it provides relief from all of the sinus pressure.

That is how to treat a sinus infection if you ask me! Has anyone else tried this?


I have often wondered how you can tell when you go from having some really bad sinus issues to a sinus infection.

I do have allergies and inflamed sinuses every once and awhile throughout the year. It doesn’t affect me much, but when it does it is usually a heck of a time.

I became so sick once that I developed a fever, headache, bloody nose and nausea, among other things. I finally went to my family doctor.

She diagnosed me with a sinus infection, gave me antibiotics and sent me on my way. However, I didn’t get away before she informed me that a bloody mucus is usually an indication that there is an infection.

So the next time that happened I went to the doctor right away, just trying to avoid all of the mess that had cropped up the time before. Guess what! No sinus infection.

I spent twenty five bucks on a co-pay to be told to go and get some over the counter meds.


My poor children have a horrible time with their sinuses on a regular basis, and it is so discouraging for me as a mother. Plus, it makes them feel badly all of the time.

Sometimes my little girl’s head will hurt so badly from her sinuses being inflamed that she can’t bear for me to touch her forehead. Her eyes hurt, as well, and her ears.

My little boy on the other hand just has the runniest nose in the world. Let him go outside, and he will come back in with a runny nose. This makes him incredibly fussy.

When both of their sinuses are acting up, it is just about enough to drive me insane. And, to top it all off, over the counter allergy medications often do not help at all. They just make them sleepy and ill.


I have a book that I turn to all the time that contains a number of natural and homeopathic cures for common ailments. One of the sinus infection cures involves breathing in a hot vapor of salt water.

My son once had a terrible sinus infection and we tried this trick. It didn't cure it but it gave him a lot of relief from the pain. The warm vapor soothes and moisturizes the sinus cavity. We ended up having to turn to antibiotics which is probably the best bet for any kind of infection, but the natural cure was a nice accompaniment to the prescription drugs.


The facts about the role of the sinus as they relate to respiration and the overall weight of the skull are really interesting to me. Once somebody points facts like this out to you they become obvious, but until then who would have thought that the sinus warm the air up for our lungs just like a drying machine.

I know that it is impossible, but I would really like to meet someone that had solid bone inside their sinus. What would their voice sound like? Would their head wobble forward or would they have an extremely strong neck? All hypothetical, but who would have thought that the sinus was so consequential.


I get a terrible sinus infection almost every winter like clock work. As soon as it gets cold and dry outside my cavities dry up and they almost always end up infected. I have seen a number of doctors trying to find some underlying cause for my condition, or trying to identify preventative measures but none of these has been effective.

For anyone that has had a sinus infection you know how debilitating this can be. You feel like your whole head is going to fall off. I usually end up out of work for a day or two and feeling less than myself for at least a week. I really wish I could find a solution but I guess that we all have to live with some pain and annoyance in our lives.

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