It’s common knowledge that under the sun’s rays we get tanner. But why? The answer is precisely the reason I nag so often about sunblock. When UV rays fall on our skin, our skin’s natural defense mechanism kick starts. Melanin offers our skin some protection from the sun and is produced by cells called melanocytes. Thus, in response to sun exposure, the melanocytes increase their production of melanin turning us a shade darker. But there is a limit to how much melanin can shield us from the sun’s UV. Under prolonged unprotected sun exposure, it can leave us with freckles and a dull skin tone.
Full article: http://dweam.com/2011/02/17/olay-white-radiance-review/