Swelling can be caused by infection, trauma, allergic reaction, or less commonly, growths or tumors.
Swelling can interfere with swallowing or breathing. If either of these occur you need to go directly to a hospital emergency room.
Infection is best treated with antibiotics, draining the abscess or both. Traumatic injuries to the face should be treated with ice packs, and professionally evaluated as soon as possible to determine if stitches or other treatment is required. Swelling is a sign of an underlying problem and should be evaluated by the appropriate health care professional.