As a skin-care ingredient, vitamin C promises everything from fading dark marks to fighting free radicals to diminishing fine lines and wrinkles. It’s incredibly effective at all of this, which is why so many people use and recommend it. It’s also why there are so many products to choose from. But alas, nothing’s perfect. Despite its efficacy, vitamin C is notoriously unstable and can quickly go from a hyperpigmentation-zapping wonder ingredient to a $60 bottle of smelly serum. To find the best formulas, we spoke to dermatologists, aestheticians, and Strategist staffers (and tested a few ourselves). Find our picks — organized by skin needs — at the link in our bio. Photo: @deiman_marcus