Surfers Ear Exostosis, or surfers ear is a bony narrowing of the external ear canal. There are usually between 3 to 5 mounds of bone that will start to grow from the surface of the canal and can begin to obstruct the ear canal.
The bone is stimulated to grow by cold water or a wet ear with wind blowing across the ear. As the bones grows water will start to get trapped behind the bones due to the narrowing of the ear canal and surface tension of water.
When you dive under the water the pressure will push the water past the bones but they will not drain because there is no force pushing the water out. The surface tension of water will not let the water leave – think of water stuck in a straw. If the water stays in the ear canal infections can develop.
It is recommended to have surgery to relieve the bony obstruction if there is water trapping and/or ear infections.