Hearing loss classification requires understanding of the anatomic site of pathology. Conductive hearing loss (CHL) involves the external ear canal, tympanic membrane, ossicular chain, or middle ear space. Otosclerosis involves abnormal bone remodeling at the oval window with stapes footplate fixation, creating a mechanical impedance to sound transmission. Cholesteatoma is a keratinizing squamous epithelium in the middle ear that erodes ossicles and can extend into the mastoid. Sensorineural hearing loss (SNHL) involves cochlear or retrocochlear pathology. Presbycusis reflects age-related loss of outer hair cells, stria vascularis atrophy, and spiral ganglion degeneration, typically producing bilateral symmetric high-frequency loss. Noise-induced hearing loss involves mechanical destruction of stereocilia and metabolic exhaustion of hair cells, characteristically producing a 4 kHz audiometric notch. Aminoglycoside ototoxicity targets cochlear outer hair cells via mitochondrial dysfunction and reactive oxygen species generation; damage begins at the cochlear base (high frequencies) and progresses apically. Cisplatin generates ROS in stria vascularis and outer hair cells. Loop diuretics alter the endocochlear potential by disrupting potassium recycling in the stria vascularis. Mixed hearing loss involves both conductive and sensorineural components. The clinician must...