Swimmer’s ear is an infection of the outer ear canal, and its primary cause is bacteria thriving in trapped moisture. Over 90% of cases are bacterial, with the rest caused by fungal organisms. About 1 in 123 people in the United States develops swimmer’s ear in a given year, making it one of the most common ear problems doctors treat.
How Moisture Leads to Infection
Your ear canal has a built-in defense system. Earwax is mildly acidic, and it produces enzymes that kill microbes before they can take hold. This thin, waxy barrier lines the canal and keeps bacteria and fungi from reaching the delicate skin underneath.
When water gets trapped in the ear canal, it softens and disrupts that protective layer. The standing moisture also raises the pH, shifting the environment from acidic to more neutral. Bacteria that would normally be kept in check can now multiply rapidly in the warm, damp canal. This is why the infection is so closely linked to swimming, but any source of prolonged moisture, including heavy sweating, humid weather, or even long showers, can set the stage.
The Bacteria Behind Most Cases
Two bacterial species account for the vast majority of swimmer’s ear infections. Pseudomonas, a water-loving bacterium commonly found in lakes, pools, and hot tubs, is responsible for 22% to 62% of cases. Staphylococcus aureus, the same bacterium behind many skin infections, causes another 11% to 34%. Most infections involve more than one type of bacteria growing at the same time.
Contaminated water raises the risk significantly. Lakes and rivers with high bacterial counts are a common source, which is why public health agencies sometimes post swimming advisories. Chlorinated pools are generally safer, but poorly maintained pools or hot tubs can still harbor Pseudomonas.
Fungal Infections Are Less Common
About 10% of outer ear infections are caused by fungi rather than bacteria. Aspergillus is responsible for roughly 90% of these fungal cases, with Candida making up the rest. If Aspergillus is the cause, you might notice yellow or black dots and fuzzy white patches in the ear canal. Candida infections tend to produce a thick, creamy white discharge instead.
Fungal ear infections are more common in tropical climates and in people who have used antibiotic ear drops for a previous bacterial infection, since killing off bacteria can give fungi room to grow.
Cotton Swabs and Other Physical Damage
You don’t need to go swimming to get swimmer’s ear. Anything that scratches or irritates the thin skin lining the ear canal can create an entry point for bacteria. Cotton swabs are one of the most common culprits. Pushing a swab into the canal strips away protective earwax and can cause tiny abrasions that invite infection.
Other objects and devices cause similar damage. Earplugs, hearing aids, and earbuds can all create friction against the canal wall, especially with prolonged use. Hairpins, fingernails, or anything else inserted into the ear carries the same risk. Even aggressive towel-drying after a shower can irritate the skin enough to break down its natural barrier.
Skin Conditions That Raise Your Risk
Eczema and psoriasis can affect the skin inside the ear canal just as they affect skin elsewhere on the body. When the canal lining is already inflamed, cracked, or flaking, it loses its ability to resist bacterial invasion. People with these conditions often deal with recurring episodes of swimmer’s ear, sometimes without any water exposure at all. Seborrheic dermatitis, the condition that causes dandruff, can have a similar effect on the ear canal skin.
A narrower than average ear canal also increases risk, simply because water drains less easily and moisture lingers longer. Anything that blocks the canal, including impacted earwax or a foreign object, traps moisture in the same way.
Other Contributing Factors
People with weakened immune systems, whether from diabetes, HIV, chemotherapy, or other causes, are more vulnerable to swimmer’s ear and more likely to develop severe infections. Radiation therapy to the head and neck can also damage the ear canal lining and reduce its ability to fight off microbes.
Soap and shampoo residue left in the ear canal can alter the pH, mimicking the effect of trapped water. Hair products and certain alkaline ear drops can do the same thing, creating conditions where bacteria thrive even in the absence of swimming.
Preventing Swimmer’s Ear
The most effective prevention targets the two main causes: trapped moisture and physical damage. After swimming or showering, tilt your head to each side and gently pull the earlobe in different directions to help water drain out. A hair dryer on its lowest heat setting, held at arm’s length, can help evaporate residual moisture.
A simple homemade preventive drop can restore the ear canal’s acidity and promote drying. Mix equal parts white vinegar and rubbing alcohol, then pour about one teaspoon into each ear before and after swimming. Let it drain back out. The vinegar restores the acidic environment that inhibits bacterial growth, while the alcohol helps evaporate trapped water. Similar solutions are available over the counter. This approach only works if you’re certain you don’t have a perforated eardrum.
Keeping objects out of the ear canal is equally important. Let earwax do its job. If you feel the urge to clean your ears, wipe only the outer ear with a towel. Wearing earplugs or a swim cap while swimming adds another layer of protection, especially if you swim frequently or in natural bodies of water.