Why do I get airplane ear and how do I prevent it?

Because the air pocket behind your eardrum cannot equalize fast enough against a cabin that changes pressure by thousands of feet in minutes. The mechanics: a narrow passage - the eustachian tube - connects your middle ear to the back of your nose and throat and opens briefly when you yawn or swallow to match middle-ear pressure to the outside. During climb and especially descent, that balancing act can lag, the pressure mismatch stretches the eardrum, and you get the fullness, muffled hearing, and pain of airplane ear. Prevention, per Mayo Clinic and the Merck Manual: work the tube before it hurts - yawn, swallow, and chew gum actively through descent (the hard phase), try the gentle Valsalva (pinch nose, blow softly), use filtered earplugs designed for flying, and stay awake for landing. Two amplifier warnings: flying congested makes equalizing much harder (a decongestant before the flight helps, per the manuals), and kids' narrower tubes explain the screaming toddlers at landing - feeding or a pacifier during descent is the pediatric trick. The flags for medical care: pain that is severe, lasts hours after landing, or comes with hearing loss or spinning dizziness.