The sinuses are air pockets located inside the bones in the skull.

They are located to either side of the nose (maxillary), behind and in between the eyes (ethmoid), in the forehead (frontal), and there is one much further back in the head (sphenoid).

(For a better understanding of this, please look at the CT scan page when you finish reading this page.)

They are probably present to reduce the weight of the skull as well as to create resonance to the voice.

The sinuses are lined with very fine hair-like projections called cilia.

The function of the cilia is to move mucus ( which is normally produced by the sinus) towards the tiny hole ( the ostium) about the size of a pin hole which provides drainage for the sinus.

Unfortunately, that hole is located at the top of the largest sinus, and consequently drainage may be poor.