Erythema multiforme (EM), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN) are skin disorders thought to be types of hypersensitivity reactions (undesirable reactions produced by a normal immune system in a presensitized host) that occur in response to medication, infection, or illness. Both SJS and TEN are severe cutaneous reactions thought to describe the same disorder, only differing in severity (TEN more severe); however, there is debate as to whether these three fall into a spectrum of disease that includes EM.