Perforated ear drum is also known as ruptured or burst tympanic membrane. There are many causes, some of which are listed below.

Otitis media. Middle ear infection is a common cause of a burst eardrum. There air which normally fills the space in the middle ear is absorbed and replaced with fluid (glue ear). If this fluid becomes infected it becomes otitis media. The pus expands, causing strain on the membrane and pain when it bursts. A cardinal sign of rupture is severe pain followed by relief and a rush of pus and blood from the ear. Ear plugs may be necessary to protect the ears from water whilst the hole heals up.
Trauma. A pointed implement such as a stick pushed down the ear canal can cause a burst eardrum.
Pressure. A sudden change in pressure such as in an aeroplane or whilst scuba diving can cause the problem. This is particularly the case in those suffering from Eustachian Tube Dysfunction. This prevents the air space in the middle ear equalising pressure with the outside world.
Surgical. This is called myringoplasty and involves creating a tiny hole in the drum with a scalpel. This is usually done to aerate the middle ear to prevent recurrent ear infections. A grommet is often placed in the hole to hold it open and stop it healing. Ear plugs may be recommended by the ENT surgeon to protect the ears from water during hair washing and swimming.

Dr Toby Bateson for zenplugs.com