Otitis externa is an infection of the ear canal caused by bacteria or fungi. It often is called swimmer's ear because it is associated with frequent swimming. Prolonged exposure to water, which may contain certain bacteria, makes the skin of the ear canal swollen and more likely to get infected. Summer humidity also changes the skin of the ear canal, increasing the possibility of infection.
While swimmer's ear is most common in the summer, it can happen any time of the year. People with skin conditions such as eczema and seborrhea may be more prone to infections. Others who are more likely to develop swimmer's ear include people who:
Suffer trauma to the ear canal, usually when trying to clean the ear with a cotton swab or other instrument
Have small ear canals that do not drain well enough on their own
Have drainage of pus from chronic middle ear infections with perforation of the eardrum
Frequently use earplugs or hairspray
Frequently get water in their ears from showers, baths or shampoos