Most cases of otitis externa occur due to bacteria invading the ear canal. If the ear canal is wet, such as after showering or swimming, it provides a hospitable environment for bacteria to grow -- hence the nickname swimmer's ear. Products such as bath soap and shampoo will similarly welcome bacteria and germs. A humid day can cause moisture to accumulate in the ear and put you at risk for otitis externa. Excessive earwax may trap moisture in the ear and raise your risk, as well.

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