This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Skin
[{'content': "A female presented with a skin lesions all over the body which shows positive 'bulla spread sign'. It is characteristic of: \nSelect and explain. \nA. Herpes gestationis, B. Bullous pemphigoid, C. Pemphigus vulgaris, D. Herpes simplex", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pemphigus vulgaris is characterized by cutaneous and mucosal blisters. On application of tangential pressure on normal skin results in formation of new bulla (Nikolsky sign) or if applied to pre-existing bulla results in the spread of bulla (bulla spread sign). Cutaneous lesions predominantly present on face, trunk, axillae, groins, and scalp. Ref: Illustrated Synopsis Of Dermatology & Sexually Transmitted Diseases By Khanna, 3rd edition, Page 64.', 'role': 'assistant'}]