What are sinuses?

The sinuses are air-filled spaces within the bones of your face that open up into the nasal cavity. They’re lined with the same membrane as your nose. This lining is called the mucous membrane and it produces a slimy secretion called mucus to keep the nasal passageways moist and to trap dirt particles and bacteria.
You have four main pairs of sinuses.

• The maxillary sinuses are in each cheekbone
• The frontal sinuses are on either side of your forehead, above your eyes
• The smaller ethmoid sinuses are behind the bridge of your nose, between your eyes
• The sphenoid sinuses are between the upper part of your nose and behind your eyes