Adults get ear infections when bacteria or fungi enter the ear and multiply, usually after something blocks normal drainage, damages the skin lining the ear canal, or traps moisture inside the ear. While ear infections are far more common in children, adults develop them through a distinct set of triggers, and the type of infection depends on where in the ear it takes hold.
Two Types of Adult Ear Infections
The ear has two main zones where infections develop, and each one has different causes. Middle ear infections (otitis media) happen behind the eardrum, in the air-filled space connected to your throat by narrow tubes called eustachian tubes. Outer ear infections (otitis externa, commonly called swimmer’s ear) happen in the ear canal itself, the passage between the outside world and your eardrum.
Knowing which type you’re dealing with matters because the causes are almost entirely different. Middle ear infections typically start from the inside, triggered by colds or allergies. Outer ear infections start from the outside, triggered by water, physical damage, or contamination.
How Middle Ear Infections Start
Your eustachian tubes connect each middle ear to the back of your throat. They serve two jobs: equalizing air pressure on both sides of the eardrum and draining fluid away from the middle ear. When these tubes swell shut or get clogged, fluid backs up behind the eardrum and creates a warm, stagnant environment where bacteria thrive.
The two bacteria most commonly responsible for middle ear infections are Streptococcus pneumoniae and Haemophilus influenzae. Both are commonly present in the nose and throat already. They only cause problems when trapped fluid gives them a place to multiply.
Several things can cause that eustachian tube blockage in adults:
- Upper respiratory infections. A cold or the flu inflames the tissue around the tube openings in the back of your throat, narrowing or sealing them shut. This is the most common trigger.
- Allergies. Seasonal or year-round allergies cause the same kind of swelling, which is why some adults get recurring ear infections during allergy season.
- Chronic acid reflux (GERD). Stomach acid reaching the back of the throat can irritate and inflame the tissue around the eustachian tube openings, contributing to dysfunction over time.
- Smoking. Tobacco smoke irritates the lining of the eustachian tubes and impairs the tiny hair-like cells that normally move mucus out of the middle ear.
Why Pressure Changes Can Lead to Infection
Flying and scuba diving create rapid shifts in air or water pressure that your eustachian tubes can’t match quickly enough. When a plane descends or you dive deeper underwater, rising pressure pushes against your eardrum and compresses the air in your middle ear. If your eustachian tubes can’t open fast enough to equalize that pressure, the result is barotrauma: pain, possible fluid buildup, and in some cases, small tears in tissue that make infection more likely.
This is why flying with a cold or sinus congestion is particularly risky. Your eustachian tubes are already partially blocked, so they’re even less able to respond to pressure changes. The combination of pre-existing swelling and physical stress on the ear creates ideal conditions for a middle ear infection to develop in the days that follow.
How Outer Ear Infections Develop
Outer ear infections follow a completely different path. Your ear canal is lined with skin that produces a thin layer of earwax, which acts as a natural barrier against bacteria and fungi. Anything that removes that protective layer, introduces moisture, or damages the skin opens the door to infection.
Water exposure is the most common cause. When water sits in the ear canal after swimming or bathing, it softens the skin and washes away earwax, creating a damp environment where bacteria flourish. Freshwater swimming in lakes, ponds, and rivers carries a higher risk than pool swimming because natural water contains more diverse bacteria.
The second major cause is mechanical damage from putting objects in your ears. Cotton swabs, bobby pins, pen caps, and paperclips can all scratch the delicate skin of the ear canal. Even tiny abrasions are enough for bacteria to enter. These objects also push earwax deeper rather than removing it, potentially trapping moisture and debris behind a wax plug. Cotton swabs in particular can cause bleeding in the ear canal and even perforate the eardrum.
Two less obvious risk factors round out the picture. Skin conditions like eczema or psoriasis affecting the ear canal create cracked, inflamed skin that’s far more vulnerable to bacterial invasion. And regular use of earbuds or hearing aids can trap warmth and moisture against the canal walls while also introducing dirt and bacteria from the devices themselves.
Symptoms Adults Should Recognize
Adult ear infections feel different from the way children experience them, partly because adults can describe their symptoms more precisely and partly because the presentation is genuinely different. The hallmark symptoms in adults are ear pain or a feeling of pressure, muffled hearing, and sometimes fluid draining from the ear (which can signal a ruptured eardrum). Children are more likely to develop fevers, balance problems, and behavioral changes like irritability and sleep disruption.
Outer ear infections tend to cause more intense, localized pain that worsens when you tug on your earlobe or press on the small flap of cartilage in front of the ear canal. The canal may feel swollen or itchy before the pain sets in. Middle ear infections produce a deeper, more diffuse pressure sensation, often with noticeable hearing loss on the affected side.
Why Some Adults Get Repeated Infections
Certain adults seem to get ear infections over and over, and the reason usually traces back to an underlying condition that never fully resolves. Chronic eustachian tube dysfunction is one of the most common culprits. If your tubes don’t open and close properly on an ongoing basis, fluid accumulates repeatedly, and each episode creates another opportunity for bacteria to take hold.
People with poorly controlled allergies, chronic sinusitis, or GERD are especially prone to this cycle. The inflammation driving their primary condition also keeps the eustachian tubes swollen and sluggish. Treating the underlying cause, whether that means managing allergies more aggressively or addressing reflux, often breaks the pattern of recurring infections.
For outer ear infections, the cycle is different. Adults who swim frequently, wear hearing aids daily, or habitually clean their ears with cotton swabs strip away protective earwax faster than the body can replace it. Without that barrier, every exposure to water or bacteria is a fresh risk. Keeping ears dry after water exposure and leaving earwax alone are the two most effective ways to interrupt this cycle.
What Happens If an Ear Infection Goes Untreated
Most adult ear infections resolve on their own or with straightforward treatment, but ignoring persistent symptoms carries real risks. A middle ear infection that lingers can cause temporary hearing loss that lasts weeks, and repeated infections can damage the tiny bones inside the middle ear, leading to longer-term hearing problems. In rare cases, infection can spread to the mastoid bone behind the ear, a condition called mastoiditis that causes swelling, redness, and severe pain behind the ear and requires more aggressive treatment.
Untreated outer ear infections can progress from mild itching and discomfort to significant swelling that narrows the ear canal completely, trapping the infection inside and making it harder to treat. In people with diabetes or weakened immune systems, outer ear infections can spread to the bone at the base of the skull, a serious complication that needs immediate medical attention.