Sunburn is the term for red, sometimes swollen and painful skin. It is caused by overexposure to ultraviolet (UV) rays from the sun. Sunburn can vary from mild to severe. The extent depends on skin type and amount of exposure to the sun. Sunburn is a serious risk factor for skin cancer and for sun damage. Because of variations in the intensity of UV radiation passing through the atmosphere, the risk of sunburn increases with proximity to the tropic latitudes. The higher the latitude, the lower the intensity of the UV rays. On a minute-by-minute basis, the amount of UV radiation is dependent on the angle of the sun. This is easily determined by the height ratio of any object to the size of its shadow. The greatest risk is at solar noon, when shadows are at their minimum and the sun’s radiation passes more directly through the atmosphere. Regardless of one’s latitude (assuming no other variables), equal shadow lengths mean equal amounts of UV radiation.