Swimming in a pool, lake, or ocean and letting the water stay in the ear can change the acidity in the ear canal, making it more prone to infection from whatever bacteria are lurking in the water.

One way to prevent "swimmer's ear," an infection of the external ear canal from the eardrum to the outside world, is to use earplugs to keep water out. You can also rinse your ears after swimming with white vinegar, alcohol, or a half-and-half solution you can make at home. And you can also buy over-the-counter products such as Swim Ear (mostly alcohol) or prescription acetic acid drops for use after swimming.

You can also learn to leave your ear wax alone. One of the biggest reasons people get swimmer's ear is overzealous attempts to remove ear wax. "Earwax waterproofs the ear canal. It should not be cleaned out," said Dr. Jennifer Smullen, an otolaryngologist at the Massachusetts Eye and Ear Infirmary.

Attempting to remove ear wax with Q-tips, bobby pins, safety pins, or even fingernails can also traumatize the canal enough to allow bacteria to penetrate the skin of the canal, causing infection, said Dr. Eli Grunstein, an associate professor of otolaryngology and head and neck surgery at Columbia University Medical Center and an attending physician at Morgan Stanley Children's Hospital in New York.

If you do get swimmer's ear, which can become quite painful, see your doctor, who will likely prescribe antibiotic drops. If your ear canal is very swollen, making it impossible for drops to get in, the doctor may insert a small "wick" that acts like a sponge to help get the drops into the canal. If the pain is severe, the doctor may also prescribe pain medication.