Stevens-Johnson syndrome, a severe mucocutaneous hypersensitivity reaction with widespread skin/mucosal blistering and sloughing, is most classically triggered by:

Stevens-Johnson syndrome (and its more severe form, toxic epidermal necrolysis) is most classically triggered by a severe drug hypersensitivity reaction (common culprits include certain antibiotics, anticonvulsants, and NSAIDs), though rare infection-triggered cases are also recognized. It's a dermatologic/mucosal emergency with significant oral involvement (severe mucositis, hemorrhagic crusting of the lips).