After passing over the turbinates, air travels through the sinuses, which are open pockets or cavities that surround the nose. The sinuses are covered by membranes that respond to the constantly changing environment.
The sinuses clean and prepare the air so that it reaches the lungs free of contaminated particles. They remove pollution (e. g., dirt, dust, or car exhaust), inflammatory agents (e. g., toxins, chemicals, or smoke), allergens (e. g., pollen, ragweed, or mold) and infections (e. g., bacteria, fungi, or viruses) that may be carried in the air.
Most people develop four pairs of sinuses: the ethmoid sinuses, which lie behind the bridge of the nose and between the eye sockets; the frontal sinuses, in the forehead; the maxillary sinuses, located in the cheeks below each eye and above the upper teeth; and the sphenoid sinuses, which are behind the nose and eyes and underneath the brain (4). Usually, we are born with only ethmoid and maxillary sinuses. The remaining two pairs develop out of the ethmoid sinuses as
we grow older. By the time we are teenagers and the rest of our bodies have physically matured, the sinuses should be fully developed.
The sizes of each of these pairs of sinuses vary, and some people have significant asymmetries within any of these pairs. One could have large or small sinuses, and some people are even missing a particular pair of sinuses or a single sinus. In fact, the sinus anatomy is so variable it is almost like a fingerprint: You can actually tell people apart based on their particular sinus pattern. As many as 15 percent of all people fail to develop one or more of their sinuses. However, people can exist quite nicely without all of them, and may live their lives without knowing that they do not have a full complement of sinuses.