How long does facial swelling usually last?

Depends: It is a function of what the underlying issue is. It could be anywhere between a few days and forever. Get it evaluated by a dentist or physician asap as infection often presents this way and can lead to serious consequences if left untreated.

Cause determines: It depends upon what is causing the facial swelling. Especially if you do not know the possible causes, it is troubling. A bruise, an allergy, a tumor, an infection, etc? The cause could be dental or medical in origin. Depending upon your other recent experiences or other symptoms, pick the most likely health care provider to start and see a dentist or a physician. Don't wait.