Ear infection, outer - Causes of otitis externa

There are several different causes of otitis externa, as well as a number of things that make it more likely to occur.

Common causes

Causes of otitis externa can include:

• a bacterial infection – usually by bacteria called Pseudomonas aeruginosa or Staphylococcus aureus
• seborrhoeic dermatitis – a common skin condition where the areas of your skin that are naturally greasy become irritated and inflamed, which can sometimes affect the ears
• a middle ear infection (otitis media) – discharge produced by an infection deeper in the ear can sometimes lead to otitis externa
• a fungal infection – such as from the Aspergillus variety and the Candida albicans variety (which also causes thrush); fungal infections are more common if you use antibacterial or steroid ear drops for a long time
• irritation or an allergic reaction – otitis externa can occur because of a reaction to something that comes into contact with your ears, such as ear medication, ear plugs, shampoo or sweat

Otitis externa can also return after previous treatment if you do not complete your course of treatment.

Possible triggers

The following things are not direct causes of otitis externa, but they may make the condition more likely to develop.

Excessive moisture

Swimming (particularly in dirty or polluted water), sweating and being exposed to humid environments can increase your risk of otitis externa because liquid in your ear canal can make you more likely to develop an infection.

Water can wash away earwax inside your ears, which can make them itchy. If you scratch inside your ears, the skin can become damaged, making the external canal more vulnerable to infection. Moisture also provides an ideal environment for bacteria – and to a lesser degree, fungi – to grow.

Ear damage

Your ear canal is very sensitive and can easily become damaged through scratching, excessive cleaning and the insertion of cotton buds. You may also damage it by incorrectly or excessively wearing hearing aids, ear plugs or ear phones.

Chemicals

Your chances of getting otitis externa are increased if you use certain products in or near your ears, such as hair sprays, hair dyes and earwax softeners.

Underlying skin conditions

As well as seborrhoeic dermatitis increasing your risk of otitis externa, underlying skin conditions such as psoriasis, eczema and acne can also increase your chances of developing the condition.

Allergic conditions

If you have allergic rhinitis or asthma, you may also be at a higher risk of developing otitis externa.

Weak immune system

If you have a condition that can weaken your immune system, such as diabetes, HIV or AIDS, or if you have been having certain cancer treatments, such as chemotherapy, you may be at higher risk of developing otitis externa. 

Inflammation

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.