Pemphigus vulgaris is a rare autoimmune disease that causes painful blistering on the skin and mucous membranes. If you have an autoimmune disease, your immune system mistakenly attacks your healthy tissues. In pemphigus vulgaris, the immune system attacks cells found in a deep layer of skin, as well as cells found in the mucous membrane (the protective lining of the mouth, nostrils, throat, genitals and anus). This causes blisters to form in the affected tissue. It’s unclear what causes the immune system to go wrong in this way. Certain genes have been linked to an increased risk of pemphigus vulgaris, but it doesn’t tend to run in families.