The function of the sinus cavities within the cranial bone (skull) is not entirely clear. Beliefs about their possible function include:
Sinus cavities allow for voice resonance
They help filter and add moisture to any air that is inhaled through the nasal passages and in the removal of unwanted particles from the sinus cavities.
Sinus cavities lighten the skull.
Sinus cavities allow space to accommodate for growth
Sinus cavities may serve as shock absorption upon trauma