Outer ear infections (otitis externa)

The ear canal

The ear canal is a tunnel of bone and cartilage which is lined by skin. This runs about 3cm from the external part of the ear to the eardrum. This allows sound to be conducted from the air to the eardrum and middle ear, without any resistance.

At the same time, the ear canal must remain clear of wax and other debris, and it must also be waterproof and antibacterial.

To achieve this, the ear canal has some very special adaptations. It is lined with skin, which in some places is extremely thin, as little as a few cells across. This is directly stuck down to the underlying cartilage and bone, unlike elsewhere in the body, where the skin is thicker and has a layer of fat underneath it. The ear canal skin migrates a fraction of a millimetre a day, growing from the centre of the eardrum and then outwards to the edges of the eardrum and along, like a conveyor belt or a slow-moving glacier. This means that the skin makes its way out of the canal naturally, carrying with it any wax or debris, rather than simply flaking off like skin elsewhere. This keeps the ear canal open and clear.

Such thin skin would normally easily waterlogged and unhealthy, and prone to bacterial colonisation without being washed- just like a belly button. But the ear canal skin is covered by a thin greasy layer which is water-repellant and acidic, making the ear canal unfavourable for bacteria to live in.

So, in most people, the ear canals remain healthy and trouble free through many years of life, with no cleaning or maintenance required.

What can cause outer ear infections?

The ear canal can become infected by bacteria when these special conditions are disrupted, which is known as otitis externa (external ear inflammation). Common causes are excessive use of cotton buds, swimming in contaminated pools and other sources of ear canal trauma, including drying the ears with a towel. In some cases, discharge from a middle ear infection into the ear canal can cause secondary infection there. Certain people may be more likely to develop these infections, for example diabetics and others with impaired immunity, and those with skin conditions such as eczema and psoriasis. Sometimes, no obvious cause is found.

What are the symptoms of outer ear infections?

Pain can be very severe, and may stop affected patients from sleeping. White smelly debris usually accumulates in the ear canals, and these can be easily blocked up with the debris, muffling the hearing.

How are outer ear infections treated?

Ear canal infections can be avoided in many cases by minimising trauma to the ear canals (from cotton buds, swimming, drying the ears with towels, etc.).

If the outer ear has been infected, treatment consists of several important steps:

• Microsuction of the ear canal, removing the skin debris with a small sucker. This is done very gently, with the help of a microscope in clinic. This may need to be repeated every couple of weeks as the ear heals.

• An ear swab can be taken to send for analysis, to identify the particular bacteria responsible for the infection.

• Antibiotic ear drops, used two to three times a day for the affected ear for 7-10 days. Click here for further details.

• Keeping the ears otherwise dry and avoiding further ear canal trauma. This is really important, so that the damaged skin does not become more waterlogged, and allowing it to heal, with return of the normal, waterproof, acidic coating to prevent further infections. There are more details here.

• Other medical problems (eg diabetes and skin conditions) should be considered, with appropriate tests if required.

Necrotising or malignant otitis externa

In rare cases, an ear canal infection may be very longstanding, and may not improve, even with ear drops and regular microsuction. A dangerous, deep-seated infection of the skin and underlying bone may be seen in diabetics, who are typically elderly, with spread of infection along the ear canal and base of the skull. This can be extremely painful. This is known as necrotising otitis externa. Suspected cases should be admitted to hospital immediately for specialist scanning and high dose intravenous antibiotics.

Skin cancers of the ear canals can also be found, sometimes with a history of repeated and prolonged ear canal infections.

While rare, these conditions should always be considered in patients whose symptoms are not improving despite treatment.