Because trapped water turns the canal into a bacterial incubator: lingering water wears down the protective wax and skin barrier, and bacteria multiply in the warm moist space - that is swimmer's ear.
The pattern: itch and fullness a day or two after swimming, then the tell - pain when the outer ear is tugged. Prevention per CDC: dry ears thoroughly after swimming (tilt, tug the lobe, towel outside only), no cotton swabs, plugs or a cap if prone. The infection itself needs prescription antibiotic drops. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper .
What to do
Common questions
Why do I get ear infections after swimming?
Because water that stays in your ear canal turns it into a bacterial incubator - swimmer's ear (acute otitis externa) is that specific infection, and swimming is its classic setup. The CDC's mechanism: water lingering in the outer canal wears down the protective wax and skin barrier and gives bacteria a warm moist place to multiply. The recognition pattern: it starts as itching and fullness a day or two after swimming, then the tell-tale sign - pain when you tug the outer ear or press the little flap in front of it - plus muffled hearing and sometimes drainage. Middle-ear infections (the kid-with-a-cold kind) are different plumbing and unrelated to swimming. Prevention is unglamorous and effective, per the CDC: dry your ears thoroughly after swimming - towel the outside, tilt each side down, tug the lobe to straighten the canal; consider a swim cap or well-fitted plugs if you are prone; never put cotton swabs in the canal (they strip the wax you need); and ask a clinician about preventive alcohol-vinegar drying drops if infections recur - but never use drops with a perforated eardrum or ear tubes. The infection itself needs prescription antibiotic eardrops - do not wait it out if pain is building.