The ear canal is usually 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 buds or fingernails can result in such a break in the barrier.
Someone who swims frequently is also predisposed to otitis externa. Prolonged exposure to moisture results in a water-resistant layer and the skin turning soft. A bacterial invasion follows.
High humidity in tropical countries like Singapore increases the risk.
Other medical conditions that lower immunity, like diabetes or cancer treatment, can also result in higher risks.