Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pemphigus vulgaris ?
    ### Response:
    Pemphigus vulgaris is an autoimmune disorder that involves blistering of the skin and mucous membranes. It occurs almost exclusively in middle-aged or older people. Many cases begin with blisters in the mouth, followed by skin blisters that may come and go.
    