Even just a little too much UV radiation and cells in human skin start to alter in unhealthy ways.
Sunshine strikes the Earth in rays of varying wavelengths.
Intermediate length rays are visible as light. UV rays contain enough energy to damage DNA in living skin and eye cells. DNA controls your cells' ability to heal and reproduce. According to NASA's ever-spinning satellites, the ozone layer's wavering protection lays four to eight percent thinner over the entire earth than it did ten years ago. A depletion of that magnitude could raise the chance of skin cancer in North America as much as 15 percent.