Pemphigus vulgaris is a severe autoimmune blistering disease caused by IgG autoantibodies against desmoglein-3 (mucosal epithelium) and desmoglein-1 (superficial epidermis), disrupting desmosomal cell-cell adhesion and causing acantholysis within the suprabasal epidermis. This produces flaccid, fragile blisters that rupture easily, leaving painful non-healing erosions. Nikolsky sign is positive (lateral pressure on normal skin causes epidermal separation). Mucosal involvement (oral, pharyngeal, esophageal, genital) often precedes skin lesions and causes severe pain, dysphagia, and nutritional compromise. Without immunosuppressive treatment, the disease is fatal from secondary infection, fluid losses, and malnutrition.