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    1. Beauty
    2. Skincare

    I Tried the New Skinfix Brighten + Firm 15% Vitamin C Serum for 30 Days

    Does the impressive formula live up to the hype?

    Hannah Baxter's avatar
    By Hannah Baxter
    Published 30 December 2025 In Buying Guides

    When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works.

    Skinfix orange bottle held by a woman with dark curly hair next to a glass beaker of orange liquid
    (Image credit: Skinfix)
    Jump to category:
    • The Formula
    • The Application
    • The Takeaway
    • Other Skinfix Products I Love
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    There are many categories of skincare that have... less than stellar clinical testing to their name. Exosomes? While buzzy with major potential, they still require a lot more research before I'm willing to incorporate them into my routine. Sheep placenta? Don't even try. But vitamin C is one tried-and-tested ingredient I'll happily use on a daily basis. After all, anything that is proven to halt signs of premature skin aging and fight free radical damage is a welcome addition to my skincare routine. However, formulating a product that not only harnesses the brightening and firming powers of the ingredient is one thing (and a lot of brands don't even come close to that), but managing to make an elegant formula that can last on the shelf (vitamin C is notoriously unstable) and minimize potential irritation? That'll make me sit up and pay attention.

    Enter, the new Skinfix Brighten and Firm 15% Vitamin C Serum, the latest launch from one of my longtime favorite skincare brands (seriously, the Triple Lipid-Peptide Cream is a dry skin savior, and every beauty editor will agree with me). I was lucky to get my hands on a bottle earlier this year to give myself adequate time to test—you might not see any significant results for at least a month with new skincare products, but likely three to four—and see whether or not the active ingredient-rich serum stacks up to its claims.

    Keep scrolling to learn whether or not the buzzy launch is worth a spot on your beauty top shelf.

    Brighten + Firm 15% Vitamin C Serum - 1 Oz

    Skinfix
    Brighten + Firm 15% Vitamin C Serum
    $69
    $69 AT SKINFIX

    The Formula

    This serum contains 15 percent THD vitamin C, an oil-soluble form that is known to have superior stability compared to some others, like L-ascorbic acid. But the hero ingredient isn't the only superstar at the skincare party. Skinfix also threw in a two percent tetrapeptide solution, which are biomimetic peptides that are clinically proven to deliver a 48 percent reductio in dark spots in 28 days. Okay, tell me more.

    Peptides—short chains of amino acids that make up essential skin proteins like collagen and elastin—are one of the buzziest ingredient categories in beauty, so I was pleased to see that there's also a two percent PGA peptide solution as well, which are stellar hydrators that also firm, plump, and strengthen the skin barrier.

    The Application

    Okay, so I'm going to be honest. The smell of this serum is... not my favorite. It kind of reminds me of that infamous hot dog water smell that is signature to Skinceutical's vitamin C serum (IYKYK), so there must be something about the ingredient that is simply kind of stinky. So if you have a sensitive nose, take caution. However, I immediately noticed that the serum left my (currently extremely dry) skin ridiculously soft upon application. It felt more like I had slathered on a rich moisturizer than a slightly watery, cream serum—I can thank the PGA peptides for that most likely.

    I used one pump every morning and that was more than enough product to cover my face and neck. If I was being super diligent, I applied another pump to my decolletage and the backs of my hands. The slightly watery texture was super easy to spread across my skin, and it sunk in fairly quickly, although I was correct to wait a minute or two before going in with moisturizer and sunscreen as there was still a bit of a tacky finish. But once the rest of my products joined in on the fun and everything dried down, there was no excessive oiliness or grease, despite the creamy feel of this serum.

    Image 1 of 3
    Hannah Baxter with bare skin and headphones
    Before (Image credit: Hannah Baxter)
    Hannah Baxter's hand with skinfix serum on the back
    Application (Image credit: Hannah Baxter)
    Hannah Baxter with bare skin and a black shirt
    After (Image credit: Hannah Baxter)
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    Hannah Baxter with bare skin and headphones
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    Hannah Baxter's hand with skinfix serum on the back
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    Hannah Baxter with bare skin and a black shirt

    The Takeaway

    Immediate results like the softness and a smooth finish are nice, but for any serum, the proof is in the longterm use. One bottle was enough to get me through about six weeks of testing if I used it every day. Of course, if you have sensitive skin (I would say I lean a little sensitive but nothing too crazy), the idea of using a vitamin C on the daily seems like irritation waiting to happen. But I'm happy to report that my skin never had a freak out—minus the ocassional bout of unrelated hormonal acne.

    I was also using this serum in the late summer into early fall when my melasma is at its worst. And while this type of pesky dark patch definitely requires the assistance of a dermatologist (at least for me) and a few Pico laser treatments, I did notice that my overall skin tone looked much more even by the tine I used the last pump. I've even started to incorporate a fresh bottle into my winter skincare routine to help enhance my skin's hydration levels, which is something I never thought I'd say about a vitamin C serum.

    Was my skin bouncier and firmer? Tough to say, but I do think that I looked pretty radiant in all 379 selfies I took between starting this product and finishing it up. I think with multiple bottles and longer term use, I'll be able to see even more collagen-boosting benefits—as much as you can get from a topical product anyway. If you want big time plumping, you can't beat an in-office laser treatment. Fraxel is my go-to, just saying...

    Truthfully, I came for the vitamin C and I'm staying for the peptide benefits. Either way, consider me the newest mega fan of the Skinfix Brighten + Firm 15% Vitamin C Serum.

    Other Skinfix Products I Love

    Triple Lipid-Peptide Cream - Full 1.7 Oz

    Skinfix
    Triple Lipid-Peptide Cream
    $54
    SHOP NOW

    A moisturizing must if the winter chill is doing its best to destroy your skin.

    Foaming Oil Cleanser - 6 Oz

    Skinfix
    Foaming Oil Cleanser
    $30
    SHOP NOW

    An incredibly unique oil cleanser that leaves my skin feeling squeaky clean but never stripped.

    Exo + Ectoin Intensive Repair Baume

    Skinfix
    Exo + Ectoin Intensive Repair Baume
    $69
    SHOP NOW

    After any kind of in-office treatment, I always reach for this reparative balm to soothe irritation and speed up healing. I'm obsessed.

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    Hannah Baxter
    Hannah Baxter
    Social Links Navigation
    Beauty Director

    Hannah Baxter is the Beauty Director at Marie Claire. She has previously held roles at The Zoe Report, Coveteur, and Bust Magazine, covering beauty, wellness, fashion, and lifestyle. She authors the Marie Claire newsletter Face Forward. Her writing has appeared in Harper's Bazaar, Allure, The Cut, Elle, InStyle, Glamour, Air Mail, Vogue, Architectural Digest, Byrdie, Nylon and more.

    She is also the founder of Anxiety Beer, a weekly newsletter about the intersection of culture and mental health. In her spare time you can catch her reading too many overdue library books, thrifting, or hanging with her hairless cat, Norman. You can find her on Instagram and TikTok @hannahbaxward.

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