There are several different causes of otitis externa, as well as a number things that make it more likely to occur. These are outlined below.
Bacterial infection
Bacterial infection is a common cause of acute otitis externa. The bacteria that cause the infection are usually either Pseudomonas aeruginosa or Staphylococcus aureus. In cases of chronic otitis externa, there may be an ongoing, mild infection, which is difficult to diagnose.
Seborrhoeic dermatitis
Seborrhoeic dermatitis is a common skin condition where the areas of your skin that are naturally greasy (sebaceous), such as the side of your nose, your forehead and your scalp, become irritated and inflamed (swollen). This may contribute to the development of otitis externa.
Middle ear infection
If you have had a middle ear infection, such as otitis media, your ear may have been producing discharge over a prolonged period of time. In some cases, the discharge may cause otitis externa.
Fungal infection
The type of fungus that can cause otitis externa includes the Aspergillus variety and the Candida albicans variety, which also causes thrush.
If you have been using antibacterial eardrops or aural corticosteroids (ear medication that relieves swelling) over a long period of time to treat another infection, you may develop a secondary fungal infection that can cause otitis externa.
Allergic and irritant reactions
Otitis externa can sometimes be caused by an allergic or irritant reaction to something that comes into contact with your ears, such as ear medication, ear plugs or shampoo. If you wear a hearing aid, you may find that it makes the inside of your ear sweaty, which sometimes can cause otitis externa.
Incomplete treatment
If you are being treated for acute otitis externa and you do not complete your treatment, you may go on to develop chronic (long-term) otitis externa.
Possible otitis externa triggers
The following things are not direct causes of otitis externa, but they may make developing the condition more likely.
Excessive moisture
You are more likely to get otitis externa if liquid gets into your ear canal. Water can wash away ear wax inside your ears making 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. The link between exposure to water and otitis externa is why the condition is often referred to as "swimmer’s ear".
Swimming (particularly in dirty or polluted water), sweating and humid environments may increase your risk of otitis externa.
Ear damage
Your ear canal is very sensitive and can easily become damaged through scratching, excessive cleaning, ear syringing 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 products that contain chemicals in or near your ears, such as hair sprays, hair dyes and earwax softeners.
Underlying skin conditions
As well as seborrhoeic dermatitis being a potential risk factor for otitis externa, underlying skin conditions such as psoriasis, eczema and acne can also increase your risk 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 weakens 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.
