Etiology of Bullous Pemphigoid No cause of bullous pemphigoid has been proved; however, the following triggers have been suggested: Drugs (including furosemide, spironolactone, omeprazole, PD-1 and PD-L1 monoclonal antibodies [eg, durvalumab, nivolumab, pembrolizumab], sulfasalazine, penicillin, penicillamine, etanercept, antipsychotics, and dipeptidyl peptidase-4 inhibitors) Physical triggers (including trauma, radiation therapy for breast cancer, UV radiation, and anthralin) Skin disorders (including psoriasis, lichen planus, and some infections) Disorders (diabetes mellitus, rheumatoid arthritis, ulcerative colitis, and multiple sclerosis) Genetic and environmental factors may play a role.