There are several different causes of otitis externa. A number of things can also increase your chance of developing the condition.
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 naturally greasy areas of your skin 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 don't complete the full course.
The following things aren't direct causes of otitis externa, but may make the condition more likely to develop.
Liquid in your ear canal can make you more likely to develop an infection. Moisture provides an ideal environment for bacteria – and to a lesser degree, fungi – to grow.
Your risk may be increased by:
- swimming – particularly in dirty or polluted water
- being exposed to humid environments
Water can also wash away earwax inside your ears, which can make them itchy.
Your ear canal is very sensitive and may become damaged through:
- scratching inside your ears
- excessive cleaning
- inserting cotton buds
- wearing ear plugs or in-ear headphones for long periods
Using a hearing aid may also increase your risk of developing otitis externa.
Your chances of getting otitis externa are increased if you use certain products in or near your ears, such as:
- hair sprays
- hair dyes
- earwax softeners
Underlying skin conditions
As well as seborrhoeic dermatitis, certain underlying skin conditions can increase your risk of otitis externa. These include:
If you have allergic rhinitis or asthma, you may be at a higher risk of developing otitis externa.
Weak immune system
You may be at higher risk of developing otitis externa if you have a condition that can weaken your immune system, such as:
Certain cancer treatments, such as chemotherapy, may also increase your risk of otitis externa.