There are three large pairs of glands (parotid, sublingual and submandibular) in your mouth that produce saliva which helps break down food as part of the digestion process.

If the duct or tube carrying saliva from the gland to the mouth becomes blocked, the gland will swell. The glands can also swell as the result of mumps, bacterial infections and certain other diseases.

If the duct is blocked by a stone, it can sometimes by squeezed or pulled out but may on occasion require surgery to remove it.