Condition	Characteristics
Bullous pemphigoid	Tense bullae with clear or hemorrhagic fluid; may begin as urticaria or pruritus with bullous formation over weeks to months; mucosal involvement rare; Nikolsky sign absent; onset typically between 60 and 80 years of age
Dermatitis herpetiformis	Clusters of pruritic and erythematous papules, excoriations, or vesicles symmetrically distributed on extensor surfaces; associated with celiac sprue; onset typically between 20 and 40 years of age
Erythema multiforme	Acute type IV hypersensitivity reaction characterized by macules, papules, and “target” lesions; begins on distal extremities and spreads proximally; minimal involvement of mucous membranes
Pemphigus vulgaris	Flaccid blisters located on head, trunk, and intertriginous areas; mucosal involvement; Nikolsky sign present; onset typically between 40 and 60 years of age
Porphyria cutanea tarda	Blistering of the skin occurring on sun-exposed areas; may exhibit hypertrichosis of the forehead and cheeks, hyperpigmentation, and urine discoloration; associated with hepatitis C, hemochromatosis, and alcoholism