The skin of the ear canal is normally protected by a waxy, water-resistant coating.
Bacteria living on the surface of the skin can cause otitis externa when there is a break in the skin’s barrier. Trauma to the skin of the ear canal from cotton-tips or finger nails can result in a break in the barrier. Someone who swims frequently is also predisposed to external ear infection. Prolonged exposure to moisture results in the water-resistant coating and skin becoming soft, allowing bacteria to infect the skin.
High humidity in tropical countries, like Singapore, ups the risk for external ear infections.
Diabetics are at higher risk due to poor immunity. They are also more prone to an aggressive form of infection called malignant otitis externa, in which the infection involves the skull bone.