What are sinuses?
There are four pairs of sinuses in the head that assist the control of temperature and humidity of the air reaching the lungs. Sinuses begin as pea-sized pouches in the newborn extending outward from the inside of the nose to the bones of the face and skull. They expand and grow throughout childhood and into young adulthood.
Eventually they become air pockets or cavities that are lined with the same kind of lining that lines the nose. They are connected to the inside of the nose through smaller openings called ostia.