Formaldehyde for middle ear infections represents one of the most short-lived therapeutic strategies in otologic history. Between the 1890s and the 1960s, physicians utilised formaldehyde therapeutically for suppurative otitis media, ideas stemming from its contemporary use as an antiseptic, and desperate clinical need in a time before reliable and broad-spectrum antibiotics. This review synthesises literature from the early 1900s to examine the scientific rationale, technique, clinical outcomes, and eventual abandonment of topical formaldehyde for the middle ear. Although early reports cited satisfactory and exciting reductions in otorrhoea and inflammatory granulation tissue, subsequent evidence demonstrated significant adverse effects, including pain, vertigo, and permanent hearing loss from ototoxicity. The emergence of safer and more targeted antiseptics, followed by sulfonamide antibiotics and penicillin, rendered therapeutic formaldehyde obsolete. Beyond its therapeutic impact, the episode offers a valuable historical lens on pre-antibiotic otology: the urgency to treat chronic infection, the willingness to adopt radical innovations, and the evolution of safety and ethical standards. Revisiting this forgotten intervention highlights the experimental landscape from which modern evidence-based otologic practice emerged.