外耳炎就是外耳道感染的炎症，英文为external otitis或 otitis externa，医学上指外耳道(external auditory meatus)至耳郭(pinna) 间之发炎反应即称为外耳炎。常因挖耳挖伤、耳朵抓伤或污水进入外耳道后所致，另耳朵皮肤炎或使用耳塞设备(如耳机、助听器等)也可能引起外耳炎，常引起外耳炎之致病菌以绿脓杆菌(P.aeruginosa)最多见，外耳炎会引起外耳道局部皮肤肿胀并伴随有疼痛感或压痛感、外耳搔痒、外耳分泌物增加。有弥漫性和局限性两种：弥漫性常侵及整个耳道，局限性即“耳疖”，中医上称“耳疔”。外耳炎还可因过敏或霉菌寄生引起，主要症状为耳道奇痒。

Otitis externa (also known as external otitis and swimmer's ear) is an inflammation of the outer ear and ear canal. Along with otitis media, external otitis is one of the two human conditions commonly called "earache". It also occurs in many other species. Inflammation of the skin of the ear canal is the essence of this disorder. The inflammation can be secondary to dermatitis (eczema) only, with no microbial infection, or it can be caused by active bacterial or fungal infection. In either case, but more often with infection, the ear canal skin swells and may become painful or tender to touch.