The skin has two primary layers: the epidermis (outer) and the dermis (inner). The epidermis has two important sublayers the stratum germi nativum and the stratum corneum. The epidermis is made up of cells called keratinocytes; these cells make up the epithelial tissue.
It is in the epidermis layer where blisters and calluses can form. Blisters occur when friction such as what might develop between the skin and the inside of a shoe-causes layers to separate within the epidermis or between the epidermis and the dermis.
As these layers separate, tissue fluid may build up, leading to a blister. While blisters often result because of fric tion, calluses result from pressure. When exposed to increased amount of pressure, mitosis will occur at a rapid rate, causing the epidermis to thicken.