Swimmer's ear is an infection in the outer ear canal, which runs from your eardrum to the outside of your head. It's often brought on by water that remains in your ear after swimming, creating a moist environment that aids bacterial growth.
Putting fingers, cotton swabs or other objects in your ears also can lead to swimmer's ear by damaging the thin layer of skin lining your ear canal.
Swimmer's ear is also known as acute external otitis or otitis externa. The most common cause of this infection is bacteria invading the skin inside your ear canal. Usually you can treat swimmer's ear with eardrops. Prompt treatment can help prevent complications and more-serious infections.