Applying salt and ice to the skin causes a painful burning sensation due to the intense cold. It may also result in frostbite or damage to the skin that is similar to a second-degree burn.
The addition of salt lowers the temperature of the ice cube. When applied to the skin, the combination rapidly leaches heat out of the surrounding skin cells, causing damage to the epidermis that is similar to a heat burn. Applying salt and ice to the skin as part of an experiment or to test pain tolerance usually doesn't result in much more than a reddening of the skin. However there have been instances when people attempting it suffered serious burns and permanent scarring.