Ask a dozen dermatologists about their favorite skin care ingredient, and you’ll likely get a dozen love letters about vitamin C. “It’s one of the few ingredients that both protects and repairs skin, but is also tolerated by a vast majority of patients,” says Dr. Titilola Sode, a board-certified dermatologist in Dallas. But not all vitamin C serums are equally effective, and the wrong formula,...

In a perfect world, we’d all wake up with clear and bright-looking skin. But even if we’re dealing with dark spots and discoloration, that doesn’t mean we can’t have the radiant, blemish-free skin of our dreams. That is, if you know which serums to look for.

According to Viseslav Tonkovic-Capin, MD, a board-certified dermatologist in Clinton, Miss., dark spots are caused by an increased number or...