So basically, the skin ensures that our internal organs are well protected. For example, if we examine one particular important internal organ in our heart, the heart is not only protected by the sternum, bone and the ribcage. It is also actually protected by the layer of skin that exists on top of our sternum and ribcage. 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.