Now, aside from actually protecting our internal organs from physical damage, our skin actually protects us from many other things. For example, it protects us from excessive UV radiation. So although our skin actually needs UV radiation to ultimately synthesize vitamin D, a hormone that is used to basically regulate calcium and phosphate ions in our blood, excessive UV radiation is dangerous. Why? Well, recall from physics that UV radiation is a type of electromagnetic wave and it carries more energy than normal visible light waves. And that's because it has a slightly higher frequency.