As big as your head! An abscess will fill with pus until the source of the infection is gone or it reaches the outside world (through your skin or gum) and pops like a zit and drains. If the source of the infection isn't taken care of the skin or gum will heal and the whole process will start over. Meanwhile, you're walking around with an infection that could affect you heart or brain and kill you. An antibiotic will only clear up the infection temporarily.