The four major types of epidermolysis bullosa simplex can result from mutations in either the KRT5 or KRT14 gene. These genes provide instructions for making proteins called keratin 5 and keratin 14. These tough, fibrous proteins work together to provide strength and resiliency to the outer layer of the skin (the epidermis). Mutations in either the KRT5 or KRT14 gene prevent the keratin proteins from assembling into strong networks, causing cells in the epidermis to become fragile and easily damaged. As a result, the skin is less resistant to friction and minor trauma and blisters easily. In rare cases, no KRT5 or KRT14 gene mutations are identified in people with one of the four major types of epidermolysis bullosa simplex .