Pemphigus is an autoimmune disease that arises when the immune system mistakenly identifies and attacks its own tissues as foreign. This misidentification leads to the formation of fluid-filled blisters, known as bullae, on the outer layer of the skin (epidermis) and mucous membranes. Normally responsible for fighting infections, the immune system, in this condition, attacks its own skin, causing tissue damage and the characteristic blisters.