1. (1) Sunburn is skin damage caused by the sun’s ultraviolet rays. (2) (Ultraviolet rays do not penetrate glass; consequently, we cannot get sunburned from sunlight shining through a closed window.) (3) When ultraviolet rays destroy skin cells, an increased amount of blood flows to the area, bringing new cells and other repair materials. (4) The red of sunburn results from this increased blood flow. (5) Sunburn hurts nerve endings in the skin send pain signals in response to cell damage.