A fluid-filled blister develops when excessive rubbing of the skin causes the epidermis and dermis to separate from each other. Blisters are rounded elevation of the skin containing clear fluid, caused by the separation of the layers of the epidermis or between the epidermis and the dermis. They are formed by forceful rubbing, burning, chemical exposure, or an infection of the outer layer of the skin especially the palm. These rounded elevations may be filled with pus, blood, or serum. They result from pressure or friction on sites such as the palms or soles of the feet.