Although otitis externa is more likely to develop when people swim in polluted lakes and rivers, it is also more common when children swim in the cleanest of pools. If the water is dirty, there is a greater risk that bacteria and fungi will be in the water in the first place, and so get into the ear. But chlorinated water can also be a problem because it can dry out the skin of the ear canal and make it easier for bacteria and fungi to penetrate. Excessive moisture or trauma are triggers When the ears are exposed to continual excessive moisture, many of the natural immune defences in the skin which line the ear canal are lost and, the ear becomes more susceptible to infection by bacteria. Fungal infections are also very common.
Some factors increase the risk.
Swimming underwater for long periods. Aggressive cleaning of ear canals with cotton buds or sharp objects like hairclips. These can scratch the skin and break down the barrier it forms against infection. Preventing further infections If your children have an infection that just won't clear up, they should take a break of a couple of weeks to let the ear heal. They should avoid getting water in the ear at all, so no swimming, shower with a shower cap pulled down over the ears, and use cotton ear plugs coated with petroleum jelly.