Swimmer’s ear may be caused by a bacterial or fungal infection. Bacteria or fungi may be introduced to the outer ear or ear canal via any number of methods. These include swimming or showering in contaminated water and introducing contaminated objects (e.g., fingers, cotton-tipped swabs, eraser-end of a pencil or pen) to the area. Exposure can also occur from simply living in a humid or moist environment. Infection can occur from just a single exposure to the infectious agent.

Swimmer’s ear is most often preceded by excess moisture in the ear, which aids the growth of bacteria or fungi. Physical trauma to the ear canal (e.g., due to forceful cleaning of the ear canal) is another common precipitator of swimmer’s ear. Chemical irritants, such as those found in shampoos, hair dyes and hairsprays, may also foster the growth of bacteria.

Children and young adults are at the greatest risk for swimmer’s ear. The infection occurs more often during the summer months, when swimming is more common. People who insert objects into their ears (including cotton-tipped swabs) are also at increased risk because they are more likely to cut the skin inside the ear. This presents an opportunity for infectious agents to penetrate the skin. People who scratch their ears often due to eczema, allergies or other conditions are more likely to break the skin, allowing infectious agents to penetrate more easily.

Other conditions that may increase the risk of swimmer’s ear include:

• Buildup of earwax that traps water in the ear
  
  
• Chronic middle-ear infections, which cause fluid buildup and may perforate the eardrum
  
  
• Immune system disorders, which make it harder for the body to fight infection
  
  
• Small ear canals that prevent proper drainage of the ear
  
  
• Allergic reaction to the plastic or rubber material used in certain ear phone devices
  
  
• Prolonged use of ear phone devices