Otitis externa develops when the external ear canal becomes susceptible to bacterial or fungal infection by various mechanisms. Sudden invasive changes in humidity from a rapid intake of water into the ear canal can predispose the external ear to bacterial infection. This occurs by thinning of the cerumen in the ear canal and weakening an important protective barrier in the ear. The epithelial surface of the skin begins to degrade, allowing easier infiltration by bacteria. The pH of the ear canal is usually maintained at 5.0 by a combination of the cerumen and the mechanical construction of the ear; when this increases it renders the ear more favorable to bacterial reproduction. Increased moisture in the ear canal can also lead to otitis externa caused by otomycosis. The buildup of fungal debris in the ear canal epithelium leads to increasing pressure and inflammation. Surfer’s ear or exostosis of the ear canal predisposes to otitis externa by rendering the ear canal more prone water-bourne pathogens. Localized trauma can cause weakening of the ear canal epithelium and thinning of cerumen, predisposing infection. Otitis externa is associated with infectious, inflammatory ear and head conditions. Gross pathology for otitis externa will include erythema of the ear canal, along with eczema-like scaly, shedding of the skin. It also includes visible ear canal swelling, as well as potentially cellulitis of the pinna and otorrhea.

Otitis externa develops when the external ear canal becomes susceptible to infection due to a variety of causes.

• Sudden invasive changes in humidity from a rapid intake of water into the ear canal can predispose the external ear to infection.^[1]
  • Prolonged exposure to moisture causes swelling of the stratum corneum.
  • The cerumen quantity in the ear canal decreases, weakening an important protective barrier in the ear.
  • The epithelial surface of the skin begins to degrade allowing increased access for bacterial infection.
  • The pH value of the ear canal, usually maintained at 5.0 by a combination of the cerumen and the mechanical construction of the ear, increases and renders the ear more favorable to bacterial infection and otomycosis.^[2]
• Increased moisture in the ear canal can also lead to otitis externa caused by otomycosis.^[3]
  • Spread of fungi results in inflammation in the ear canal.^[3]
  • The buildup of fungal debris in the ear canal epithelium leads to increasing pressure and inflammation.
  • Extensive use of topical antibiotic ear drops to treat bacterial otitis externa increases predisposition to otomycosis.
• For immunocompromised individuals, chronic or recurrent otitis externa from bacterial infection results from the spread of infection to the temporal bone.^[4]
  • Spread of infection may proceed through the temporal bone to the cranium.

• Surfer’s ear or exostosis of the ear canal raises the predisposition to otitis externa by rendering the ear canal more prone to trapping water and water-bourne pathogens.^[5]

• Localized trauma can lead to otitis externa from the following dermatoses. Weakening of the ear canal epithelium and thinning of cerumen predisposes infection in the following dermatoses:^[6]
  • Eczema
  • Seborrhea
  • Psoriasis
  • Contact dermatitis

• Otitis externa is associated with the following infectious, inflammatory ear and head conditions:
  • Otitis media
  • Osteitis
  • Osteomyelitis^[7]
  • Otorrhea^[8]
  • Otalgia

• Gross pathology for otitis externa will include erythema of the ear canal, along with eczema-esque scaly, shedding of the skin.^[9]
• Ear canal swelling will be visible.
• Cellulitis of the pinna and otorrhea may also be present upon physical examination.^[10]