No matter which skin issues you’re currently bemoaning, chances are your routine could benefit from a vitamin C serum. The antioxidant is one of the few skin care ingredients dermatologists will back for its noticeable brightening, protective, and collagen-boosting properties. “Vitamin C is an antioxidant,” says dermatologist Kenneth Howe, M.D., at Wexler Dermatology. “When ultraviolet light penetrates your skin, it causes lasting damage by producing free radicals. Vitamin C can prevent that damage by ‘quenching’ the free radicals as they form.” There’s just one caveat: “It has to be present within the deeper layers of your skin in order to do that.”

This is the main reason derms will often tell you to get your daily dose of vitamin C in serum form. “They typically have the highest concentration of active ingredients,” says Howe. In order to get maximum results, though, you’ll need these highly concentrated actives to be properly formulated. You might have heard experts debating the merits of various forms of the power ingredient. Here’s one to memorize: L-ascorbic acid. “It’s a pure form of vitamin C,” says dermatologist Joshua Zeichner, M.D.. “It’s typically highly unstable, so it must be adequately protected from sunlight and capped at an acidic pH.” Howe’s preferred form is also L-ascorbic acid, which he says penetrates more deeply than other forms, making it more likely to reach the layers of skin where you actually need it to work. And that’s not all you need to think about it when it comes to the best vitamin C serums; you’ll also want to consider its concentration.

“You should look for serums that contain 10% to 20% vitamin C,” says dermatologist and cofounder of LM Medical, Morgan Rabach, M.D. “Less than 10% is not as effective and over 20% causes more skin irritation.” A supporting cast of characters can also boost its efficacy. “Vitamin E stabilizes vitamin C for maximum skin protection, and ferulic acid helps lower the pH level of vitamin C so your skin can use the vitamins easily,” she says. “I also look for darkly tinted glass bottles with airless delivery, as air causes vitamin C to degrade.”

It seems like a lot to remember, so we did the heavy lifting of finding out where those multiple factors intersect. Below, the 17 best vitamin C serums (or products with serum-like textures, to use the term more generously) that meet this stringent list of criteria. Scroll through to find out which bottle delivers on a budget, which is perfect for packing in your carry-on, and which meets every single derm’s approval.