What causes an ear drum to burst?

Either...: ...High pressure behind it, as with an ear infection, or, also with an ear infection, enzymes made by bacteria can eat right through the eardrum. Also, slapping the ear, or poking in it (even with a q-tip) can break through the eardrum.

Pressure: When a child gets a middle ear infection (acute otitis media) pressure builds up in the middle ear space which now has pus as well as the air that is normally there. The eustachian tube (tube between the middle ear and nose) is usually blocked with an ear infection and the increased pressure from the pus & air can eventually burst the ear drum, which connects the middle ear to the external ear.

Pressure: When one gets a middle ear infection, or "otitis media, " fluids build up behind the ear drum. The fluid becomes infected as the bacteria that normally live in our ear fluid multiply. As the infected fluid continues to accumulate, it pushes on the eardrum. As the eardrum is a relatively thin membrane, it can perforate or "burst" from the pressure.