The mastoid process is a bony projection located below the external ear canal. It provides attachment points for neck muscles and contains air cells. In infants and children, the mastoid process is not fully developed and contains softer bone, making the nearby facial nerve more vulnerable. As the mastoid process grows and the air cells develop during puberty, it provides more protection for the facial nerve. Mastoiditis is an infection of the mastoid air cells that can develop from a middle ear infection. It causes ear pain, discharge and tenderness and is usually treated with antibiotics or surgery.