email. Knowledge center. Blisters are small pockets of liquid that form on the outer layer of the skin after the skin becomes damaged (usually caused by forceful rubbing or burning). Blisters prevent the area from becoming further damaged by protecting the skin underneath and giving it adequate time to heal.listers on feet caused by running without shoes. 1  Friction or rubbing on the skin-intense friction or rubbing on the skin can result in the formation of a blister if it continues for long enough.