Humans need sunlight to help keep their bones, blood and other body systems healthy, but too much time in the Sun can sometimes leave people with a sunburn. Sunburns often strike when the body gets too much of a type of light, called ultraviolet light, from the Sun. As your body recognizes there is too much ultraviolet light, it turns on a defense system. The immune system, which responds to invaders like viruses and other harmful things like ultraviolet light, kicks in. Some people might see their skin get red or blistered. They might feel itchy or painful. But not everyone experiences sunburn in quite the same way. A big part of the answer to your question also has to do with human cells. My friend Cynthia Cooper, a researcher at Washington State University, knows a lot about cells and how they work. Read More ...