A number of things can cause the eardrum to rupture. One of the most common causes is an ear infection. Another common cause is poking the eardrum with something like a cotton-tipped swab or a bobby pin that you're using to try to clean wax out of your ear canal. (Don't do that!) Sometimes children can puncture their own eardrum by putting objects such as a stick or a small toy in their ear. It can also happen because of air pressure changes, like when you're on a plane that's climbing or descending or when you scuba dive. Head injuries can also be a cause.