Pro makeup artist Molly Stern says primers are meant to serve as a layer between skin and foundation to create a more even surface. But not everyone needs them. "The best candidate for them would be someone who is very oily or has a lot of scarring from acne," she says. But do primers actually make a difference? We had two women of different ages each test a top foundation primer geared toward their skin type. Find out if their makeup looked better ... and if anyone noticed.