Answer: Ultraviolet
Explanation: You know how when you buy sunscreen, the panels on the bottles always talk about UV/UVA protection? That's because the sun radiates energy in the form of ultraviolet rays, which can be harmful to the human body if we get too much of it. Most dermatologists suggest wearing sunscreen to protect from overexposure, because you can't see sun damage until it's too late (because UV rays aren't visible to the nake eye).