Otitis externa
Inflammation of the skin lining the ear canal, usually triggered by moisture or trauma disrupting its protective acid mantle, treated topically because the problem is a superficial skin infection rather than a deep-seated one.
First principles
The ear canal skin normally defends itself, and otitis externa is a breakdown of that defence
The external auditory canal is lined by skin that produces cerumen (earwax), which is mildly acidic and water-repellent, forming a protective barrier against bacterial and fungal overgrowth. Anything that disrupts this barrier, water exposure (swimming, humid climates), trauma from cotton buds or scratching, or skin conditions such as eczema and psoriasis, raises the local pH and strips protective wax, allowing normal skin commensals and opportunistic organisms (chiefly Pseudomonas aeruginosa and Staphylococcus aureus, or fungi such as Aspergillus and Candida) to overgrow and invade the skin, causing inflammation of the canal.
Educational content pending clinical review. Not medical advice.