Drug eruptions are common mucocutaneous adverse reactions encountered across all medical specialties, occurring in approximately 0.1-1% of patients exposed to medications. However, accurate diagnosis and identification of the culprit drug remain challenging because of heterogeneous clinical presentations and a wide range of differential diagnoses, particularly viral exanthems. Comprehensive evaluation of medication history, infection status, latency period, and clinical phenotype is essential for appropriate narrowing of suspected agents. Among drug eruptions, Stevens-Johnson syndrome and toxic epidermal necrolysis represent life-threatening, rapidly progressive conditions in which early recognition is critical; mucosal erosions, skin pain, fever, and systemic organ involvement should prompt immediate suspicion. Identification of the causative drug is crucial not only for preventing recurrence but also for preserving future therapeutic options. Diagnostic modalities-including the drug-induced lymphocyte stimulation test, skin testing, and drug provocation testing-should be selected based on clinical phenotype, disease severity, and timing. A structured, time-conscious diagnostic strategy may reduce inappropriate drug allergy labeling and facilitate safer long-term pharmacotherapy.