Otitis externa (OE) is inflammation of the soft tissue of the outer ear and external ear canal, typically caused by an infectious process. It is most commonly bacterial and sometimes fungal in nature. The most common bacterial pathogens include Pseudomonas aeruginosa and Staphylococcus aureus. OE can also be caused by noninfectious dermatologic processes.

Patients with OE present with severe ear pain with tenderness on palpation of the external ear. Other symptoms include erythema, edema, hearing loss, pruritus, and discharge. OE is also known as swimmer's ear, as it is historically seen in those who have spent time in water, but it can also be seen in diabetic individuals.

The etiology of OE includes disruption of normal protective barriers such as cerumen, which serves as a mechanical barrier and acidifies the ear, helping inhibit infection. Entry of water, bacteria, or other debris into the ear canal is a major contributor to formation of infection. Other risk factors include ear trauma, scratching, swabbing, hearing aids, earphones, earplugs, or any foreign body insertion, as these create conditions under which bacterial infection can spread. Furthermore, OE can manifest in environments with high humidity or secondary to perspiration. It is seen in patients with chronic dermatologic conditions including eczema, psoriasis, acne, and seborrheic dermatitis, and in patients who have undergone radiation therapy, which can damage cerumen production.