“The goal with brightening serums isn't to lighten the overall skin tone, but rather, create an even skin tone by reducing overactive areas,” says Dan Belkin, ...

The main difference between using a serum and a facial oil is that oil molecules are much larger and can only penetrate the outermost layers of the skin. ... ...

Also, once you buy your serum, it is a good idea to reduce it regularly and every day, since active ingredients tend to expire faster. So it's just a waste of ...