My apologies to those of you from Brazil, Australia, South Africa, and other countries that are heading into the winter months. If you are a summer lover, take comfort in knowing that this information will be useful to you in not too many months. Swimmer's ear is an infection of the skin lining the ear canal. Bacteria normally live on the surface of this skin with no ill effect. If the ear is wet for a long period of time, the skin can become prune-like in the same way one's fingers and toes become soft and wrinkled when they are in water for a long period of time.
Bacteria can easily move into the soft skin.
The skin can even be breached as a result of the ear's becoming extraordinarily dry, causing the skin to crack. Ironically, swimmer's ear can be the result of spending time in desert conditions. Swimmer's ear is more common in people who spend time in swimming pools than in people who swim in lakes. This is thought to be because the chlorine in swimming pools kills the good bacteria in the ear fairly effectively, but is not as effective against the harmful bacteria hiding in the ear canal. For unclear reasons, swimmer's ear is not common in infants.