CD40LG and autoimmune bullous skin disease: Taken together, the present study describes IgM pemphigoid as a distinct and potentially underdiagnosed clinical entity characterized by (1) exclusive anti‐BMZ IgM autoantibodies by direct IF microscopy, (2) serum IgM reactivity against the epidermal side of salt‐split skin, (3) BP180 as main target antigen, (4) a predominantly non‐bullous phenotype in the absence of mucosal involvement, and (5) a rather mild disease course.