Q. I had really painful swimmer's ear last weekend. What causes this, and how can I treat it?

A. Swimmer's ear, or otitis externa, is especially common in warm, humid climates like Hawai'i's or in folks with eczema of the ear canal. It is often caused by the germs Pseudomonas aeruginosa or Staphylococcus aureus. Fungal infections can occur after prolonged use of antibiotics. Infection with Candida sometimes occurs in folks who use hearing aids. Water in the ear canal increases germ growth. But the use of cotton swabs is a major culprit; they can cause tiny microscopic cuts through which germs can enter and cause a painful infection. There's a good chance you have otitis externa if it hurts when you pull on your ear.

One thing you can do is leave your ears alone. Earwax is acidic, which inhibits bacterial and fungal growth. It is also hydrophobic, repelling water away from the skin. Earwax therefore protects the skin from pathogens and contains natural antibiotics. Cleaning or scratching the ear canal not only removes protective earwax, but also cause abrasions in the thin ear canal skin, exposing the deeper tissues to invasion by germs.

And there's no need to clean out earwax — the skin of the canal normally grows outward like a moving sidewalk, periodically dropping wax outside. Cotton swabs often push earwax further in, making things worse. Things that occlude the canal like hearing aids, headphones, or diving caps can predispose to external otitis. Removing moist debris from the canal (aural toilet) is the single most important aspect of treatment, as it enhances healing and the penetration of antibiotic ear drops into infected areas. Don't swim for seven to 10 days, and put a cotton ball coated with petroleum jelly in the ear canal while bathing. Combined acetic acid and aluminum acetate otic (like Domeboro Otic) works just as well as antibiotic ear drops. Acetic acid has antibacterial and antifungal activity, while aluminum acetate helps to reduce itching, stinging and inflammation.

Use ear drops correctly: Tilt your head toward the opposite shoulder, pull the ear upwards, and fill the canal with drops. Lie on your side for 20 minutes or place a cotton ball in the ear canal for 20 minutes to maximize antibiotic penetration.

To prevent future infections, buy Swim Ear or make your own solution: two parts alcohol and one part white vinegar, and put five drops into the ear whenever water gets in (from showering, swimming, etc.) to chemically dry the ear out. Alternatively, you can use a blow dryer.

And remember: No cotton swabs!

Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i-Manoa John A. Burns School of Medicine. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.