A 25-year-old swimmer presents with a red, painful external ear canal after spending several hours in the pool every day for the past week. Based on these symptoms, what is the most likely diagnosis.

Choice A rationale A perforated eardrum involves a tear or hole in the tympanic membrane, often resulting from trauma, sudden pressure changes, or a severe middle ear infection. While it can cause pain and hearing loss, it is not typically associated with a red and painful external canal after swimming. The history of frequent water exposure strongly points toward an external ear pathology rather than a structural rupture of the membrane separating the middle ear. Choice B rationale Eustachian tube dysfunction occurs when the tube connecting the middle ear to the nasopharynx fails to open or close properly. This leads to pressure imbalances, a feeling of fullness in the ear, and muffled hearing. It does not cause inflammation or redness of the external ear canal. This condition is frequently linked to upper respiratory infections or allergies rather than the bacterial or fungal growth seen in swimmers with external canal irritation. Choice C rationale Acute otitis media is an infection of the middle ear space behind the tympanic membrane, common in children and often following a cold. It typically presents with a bulging, erythematous eardrum and deep-seated ear pain. Because the infection is internal, the external canal itself usually appears normal unless the eardrum has ruptured. The patient's history of swimming suggests an issue with the outer canal rather than the middle ear. Choice D rationale External otitis, commonly known as swimmer's ear, is an inflammation or infection of the external auditory canal. Frequent exposure to water can disrupt the protective cerumen barrier and alter the acidic pH of the ear canal, creating an environment ripe for bacterial growth, often Pseudomonas. Symptoms include significant pain when the pinna is moved, redness, and swelling of the canal. Given the patient's swimming history and localized external pain, this is the most likely diagnosis.