We independently evaluate all of our recommendations. If you click on links we provide, we may receive compensation. Shopping Beauty Products Skincare The 15 Best Vitamin C Serums of 2024 Tested by PEOPLE We've never gotten so many compliments on our skin By Bianca Lambert Bianca Lambert Bianca Lambert has been writing for PEOPLE since 2022. She is also a contributing writer for Byrdie specializing in natural hair and skincare. She has worked as a freelance beauty and travel writer for over four years. Bianca graduated with a degree in Television Broadcasting from Middle Tennessee State University. She started her career at BuzzFeed in Los Angeles, where she worked as a Style and Beauty Video Producer, before taking a role as Social Video Coordinator. After two years in the world of video, she currently resides in Los Angeles and works as a freelance writer and creative producer. People Editorial Guidelines and Cai Cramer Cai Cramer Cai Cramer is a shopping writer at PEOPLE.com with 2 years’ experience in journalism and digital media. She regularly tests the best and buzziest products in the beauty and lifestyle spaces and has researched and written about moisturizers, blow dryers, clothing, and luggage, among many other popular products. People Editorial Guidelines Updated on September 18, 2024 01:58PM EDT In This Article View All In This Article Our Top Picks Reviews Add to Cart What to Know Behind the Scenes FAQ Why Trust PEOPLE? What Is People Tested? Photo: People / Kristin Kempa Vitamin C is one of the most searched skincare ingredients on the internet. Rightfully so, given the number of products on the market and the fact that the powerhouse ingredient actually yields visible results. The More You Know Vitamin C is clinically proven to protect against sun damage while boosting collagen and minimizing wrinkles — making it a popular active ingredient in eye serums and other skincare products. "Translated to real life, vitamin C is a workhorse for looking great," Dr. Christina Lee Chung, board-certified dermatologist at Schweiger Dermatology Group, tells PEOPLE. However, to get benefits like improving wrinkles, evening out skin tone, and helping with skin sagging, Chung says consistency is key — so using vitamin C daily can be a game-changer for your skin. PEOPLE tested 32 vitamin C serums for six weeks, and, honestly, we were blown away by the brightening and firming abilities of the following skincare products. Our Top Picks Best Overall: SALE L'Oreal Paris Revitalift Vitamin C Face Serum at Amazon $36 $21 Jump to Review Best Overall, Runner-Up: SkinCeuticals C E Ferulic at Dermstore $182 Jump to Review Best Budget: Yes To Grapefruit Brightening Serum at Amazon $15 Jump to Review Best for Combination Skin: SALE TruSkin Vitamin C Facial Serum at Amazon $49 $38 Jump to Review Best for Fighting Sun Damage: Herbivore Brightening Serum at Amazon $65 Jump to Review Best for Mature Skin: Klur Brilliant Light Repair Serum at Amazon $199 Jump to Review Best for All Skin Tones: BeautyStat Universal C Skin Refiner at Amazon $85 Jump to Review Best for Immediate Glow: SALE Olay Vitamin C Peptide 24 Serum at Amazon $30 $20 Jump to Review Best for Dark Spots: Goodal Vitamin C Dark Spot Serum+ at Amazon $21 Jump to Review Best for Sensitive Skin: CeraVe Skin Renewing Vitamin C Serum at Walmart $24 Jump to Review Best Overall L'Oreal Paris Revitalift Vitamin C Face Serum PHOTO: Target $36 $21 at Amazon $30 at Walgreens View on Lorealparisusa.com Star Qualities Just as effective as products that are double the price Drastically improved our skin over the course of a few months Tube shape allows you to get every last drop Glides onto the skin easily without feeling sticky or weighed down Red Flags Results weren’t immediate, but we did notice them over time Drugstore products are competing with pricier options and becoming best in class. This fragrance-free anti-aging serum features 10 percent vitamin C, with over 3,500 users giving five-star ratings of the fast-absorbing, skin-mattifying formula after seeing visible results. During our tests, we found that while the serum didn’t yield immediate results like other serums we tried, it offered longer-lasting results. Over the course of a few months, this L'Oreal serum drastically improved our tester's skin's radiance. “I've paid this much for other vitamin C serums that were half as effective, so I think this is a great price for this product," she said. On top of that, this serum melted into the skin without any stickiness or added weight and had an immediate glowing and smoothing effect. Plus, unlike pump containers, the L'Oreal Revitalift tube shape prevents you from wasting any serum because you can squeeze every last drop out of this affordable product. Size: 1 oz. | Key Ingredients: 10% vitamin C, hyaluronic acid, retinol | Skin Type: All People / Samantha Jones Pro Tip Stick with a 10 percent vitamin C concentration if this is your first experience with the antioxidant or if you have sensitive or reactive skin. You can always work your way up to a higher concentration. Best Overall, Runner-Up SkinCeuticals C E Ferulic PHOTO: Bluemercury $182 at Dermstore $182 at Skinceuticals.com $182 at Bluemercury.com Star Qualities Improves skin texture while boosting radiance Works well with other skincare products that might already be part of your routine Doesn't leave a sticky residue Red Flags It has an odd sour-like scent upon application If you ask anyone serious about their skincare routine, it's very likely this is (or has been) in their rotation as it is the gold standard of vitamin C serums. It's patented and clinically proven to reduce combined oxidative damage from free radicals generated by UV, ozone, and diesel exhaust by up to 41 percent. Additionally, the serum improves signs of lines and wrinkles while boosting radiance and even fading dark spots. Not only did it make our skin glow, but it also smoothed fine lines and texture on our skin. It also pairs well with other products you may already have in your routine and doesn't leave a sticky residue. We do want to point out that our tester, who has used vitamin C daily for eight years, wasn’t expecting a notable difference. However, she was pleasantly surprised: “I ended up seeing a difference in the texture of my skin and fine lines during this six-week test. Everything is a bit smoother and softer — this is the only product/step that changed.” One other thing we noticed about this product is the odor, but that won't stop us from brighter skin. Size: 1 oz. | Key Ingredients: 15% pure vitamin C (L-ascorbic acid), 1% vitamin E, 0.5% ferulic acid | Skin Type: All, including sensitive People / Shannon Bauer Best Budget Yes To Grapefruit Brightening Serum PHOTO: Amazon $15 at Amazon $27 $15 at Walmart $15 at QVC Star Qualities It only took a few days to reap the benefits of this serum Formulated with over 95 percent natural ingredients Red Flags It has a strong fragrance, which may not be for everyone This Yes to Grapefruit serum boasts PHAs that gently exfoliate and vitamin C to boost radiance. In our testing, we saw results in just a few days. This serum was refreshing, not greasy or sticky, and it imparted a subtle glow upon application. It can be used morning or night, but we prefer to use it in the morning for the light grapefruit scent and instant skin-radiance boost. However, if you prefer non-scented serums, you should opt for another pick on our list. Size: 0.95 oz. | Key Ingredients: Vitamin C, 5% polyhydroxy acids | Skin Type: Dry PHOTO: People / Allison Vancura PHOTO: People / Allison Vancura PHOTO: People / Allison Vancura Best for Combination Skin TruSkin Vitamin C Facial Serum PHOTO: Amazon $49 $38 at Amazon $22 at Target $40 $19 at Walmart Star Qualities Absorbed in just 30 seconds Extremely hydrating formula Our skin was glowy for up to 12 hours Red Flags The vitamin C percentage is not listed In testing, we found that this serum was absorbed in just 30 seconds and was hydrating enough to use on combination skin without the need for any additional moisturizer. One of our testers said she started receiving compliments on her skin's complexion and credits that to this product. "I'm way more confident in stepping outside without any makeup. I took a selfie after flying on a 13-hour flight and my bare skin still looked bright and glowy," she adds. The vitamin C percentage is not listed, so those who are new to vitamin C or anyone with sensitive skin should test a small amount of the product on your skin first before applying it to your face. Size: 1 oz. | Key Ingredients: Vitamin C, vitamin E, and hyaluronic acid | Skin Type: All People / Emily Cieslak Best for Fighting Sun Damage Herbivore Brightening Serum PHOTO: Herbivore $65 at Amazon $65 at Nordstrom $65 at Sephora Star Qualities 15 percent vitamin C effectively brightened dark spots Didn’t irritate our sensitive-skinned testers Antioxidant-rich turmeric evened out skin tone Red Flags Light gingery scent from the added turmeric, but we found it pleasant By now, anyone who’s tapped into the skincare world (and many who aren’t) probably know about the damaging effects of sun exposure on the skin, which can cause dark spots, fine lines, and scarring. This serum aims to combat these common concerns with a high percentage of stable vitamin C and turmeric, an ingredient that’s packed with antioxidants. Even our testers with the most sensitive, rosacea-prone skin agreed that this serum did not sting or tingle upon application. The product is formulated without any additional fragrance (another win for the sensitive skin community), but the turmeric does give it a slight gingery smell. It has a light, creamy texture that sank into our skin like a thin moisturizer, leaving behind a subtle, lit-from-within glow. Size: 1 oz. | Key Ingredients: 15% THD vitamin C, turmeric | Skin Type: All These Are the Best Face Sunscreens We Tested in 2024 Best for Mature Skin Klur Brilliant Light Repair Serum PHOTO: Klur $199 at Amazon View on Klur.co $88 at Credo Beauty Star Qualities Absorbs into the skin quickly and works well with other skincare products Testers with mature skin saw firmed skin over time Felt instantly hydrating Red Flags It's on the expensive side, but a little bit goes a long way Formulated with a blend of 20 percent bioavailable vitamin C in tandem with a skin-strengthening and calming complex of plant extracts to help even skin tone sans unwanted irritation, this clean formula absorbs in seconds and, for some skin types, even helps control excess oil production. We found the Klur Vitamin C Serum to be super hydrating and smoothing upon application. Plus, our tester noted that her 63-year-old skin felt firmer over time. It's expensive, but a little bit goes a long way. Size: 1 oz. | Key Ingredients: 20% bioavailable vitamin C | Skin Type: All PHOTO: People / Nellah McGough PHOTO: People / Nellah McGough Best for All Skin Tones BeautyStat Universal C Skin Refiner PHOTO: Amazon $85 at Amazon $85 at Nordstrom $85 at Nordstrom BeautyStat is a skincare company founded by cosmetic chemist Ron Robinson, and the brand’s hero product, the Universal C Skin Refiner, was the very first serum to include 20 percent stable vitamin C (meaning it won’t oxidize or change colors). The brightening formula was created to work on all skin types, textures, and tones. The formula includes a powerful 20 percent concentration of vitamin C, so sensitive-skinned folks should tread lightly at first, applying the serum twice a week in the mornings before moving on to more regular application. The texture is smooth and slightly mattifying, and it easily blends into the skin without leaving any sticky residue behind. Editors Say “I swear by the Universal C Skin Refiner for lightening acne scars and hyperpigmentation. I have sensitive, rosacea-prone skin, so I started by applying the formula about twice a week before increasing use to every other day. My skin has brightened so much since I started using it!” —Cai Cramer, PEOPLE shopping writer Size: 1 oz. | Key Ingredients: Vitamin C, squalane, green tea | Skin Type: All People / Samantha Stevenson Best for Immediate Glow Olay Vitamin C Peptide 24 Serum PHOTO: Target $30 $20 at Amazon $30 at Target $40 at Ulta Star Qualities Made our skin look instantly luminous Visible improvement in the hydration and radiance of our skin Our skin still felt refreshed hours after application Red Flags Vitamin C percentage is not listed Olay is a skincare brand staple. If scent is a vital factor in your skin products, you'll love that this serum wakes up your senses and boosts radiance in the skin. If you're looking for a serum with peptides, this one is formulated with vitamin C, skin barrier protecting niacinamide, and hydrating peptides. The citrus-scented formula is clinically proven to help skin look visibly more hydrated in one day and more radiant after one month. We loved that this serum resulted in visible hydration and radiant-boosting effects and even after several hours, our skin remained feeling refreshed. It had an immediate glowing effect, but it faded within an hour, so if glowing skin isn't your top priority, but feeling refreshed and hydrated is, this is a great value pick. We absolutely love the scent but realize it may not be for everyone, especially those with fragrance sensitivities. Size: 1.3 oz. | Key Ingredients: Vitamin C, niacinamide, peptides | Skin Type: All PHOTO: People / Nicole Harris PHOTO: People / Nicole Harris Best for Dark Spots Goodal Vitamin C Dark Spot Serum+ PHOTO: Amazon $21 at Amazon $27 $25 at Target $28 at Yesstyle.com Star Qualities Contains skin barrier-protecting and collagen-boosting ingredients Significant improvement in skin tone and texture in just a few days Diminished dark spots over time Red Flags The vitamin C percentage is not listed Finding the right vitamin C to fade dark spots can take a lot of trial and error. (And we all know that can get expensive.) However, this dark spot serum is relatively budget-friendly and is packed with a powerful blend of fresh green tangerine extract (an ingredient that offers 10 times more vitamin C than lemons), niacinamide, and arbutin that helps improve dark spots and post-acne hyperpigmentation. It also has centella asiatica (tiger grass) to protect the skin barrier and boost collagen. After only a few days of using this product, we saw a reduction of dark spots. While the tangerine scent might not be for everyone, our skin felt healthier, more radiant, and clearer after just a few days, and we think this product is an absolute steal. Size: 1.01 oz. | Key Ingredients: Vitamin C, centella asiatica, niacinamide, arbutin | Skin Type: All, including sensitive Best for Sensitive Skin CeraVe Skin Renewing Vitamin C Serum PHOTO: Amazon $24 at Walmart $30 at Ulta View on Instacart.com Star Qualities Lightweight and easy to apply Reduction in post-breakout hyperpigmentation and fine lines Lower concentration of vitamin C, which makes it safer for sensitive skin Red Flags Packaging is tricky to open Drugstore products may offer more budget-conscious prices, but that doesn’t mean they’re any less effective. For sensitive or breakout-prone skin, this dermatologist-developed and allergy-tested formula has all the necessities that lead to healthier, radiant skin — including 10 percent L-ascorbic acid, hyaluronic acid, skin barrier-protecting ceramides, and soothing vitamin B5. Our tester loved its lightweight formula and said she will continue to use it at home until the very last drop. She did note that the packaging can be tricky — the cap was a bit confusing to remove. But while using, her acne-prone skin with post-breakout hyperpigmentation saw a reduction in the appearance of those spots while the formula felt light on the skin. She even noticed a reduction in fine lines around her mouth area. Size: 1 oz. | Key Ingredients: 10% pure vitamin C (L-ascorbic acid), ceramides, hyaluronic acid, vitamin B5 | Skin Type: All Best for Dry Skin Sephora Collection Super Glow Serum with Vitamin C+E PHOTO: Sephora $40 $28 at Amazon $28 $21 at Sephora $21 at Kohls.com Star Qualities Noticeable, dewy results in just a few weeks Formulated with 97 percent ingredients that are naturally sourced Greatly improved the firmness and smoothness of the skin in just a few weeks Red Flags Not great for those with oily skin If natural ingredients are your jam, we have some good news. This fast-absorbing serum is made with 97 percent naturally sourced ingredients, including natural forms of vitamins C and E alongside peptides derived from marine algae that firm and hydrate to combat and smooth wrinkles. In testing, we saw dewier and healthier skin in just a few weeks. Of all the serums we tested, this one definitely had a "wow" factor, and our tester felt that her skin looked younger after using this product for a few months. However, if you have oily skin, this might not be the best serum for you, and it's packaged in a glass bottle, which made our tester a little nervous that she might shatter it at any moment. But from our standpoint, this product, which provided a vast skin improvement from a non-plastic bottle is a fantastic deal. Size: 1.01 oz. | Key Ingredients: Vitamin C, vitamin E, natural peptides from marine algae | Skin Type: Dry, balanced PHOTO: People / Cynthia Sanz PHOTO: People / Cynthia Sanz Best for Clogged Pores InnBeauty Project Vitamin C + Green Superfoods Jelly Serum PHOTO: Sephora $48 at Amazon $38 at Sephora $80 at Walmart Star Qualities Helped dissipate acne flare-ups Felt refreshing on our skin Has a non-comedogenic formula, meaning it won't clog pores Red Flags The vitamin C percentage is not listed If you're an oil lover or somewhere in between, a serum-oil hybrid feels like an ideal match. This serum is like a lush smoothie for your face that won't clog pores — though our tester shared the formula didn't completely stop acne from occurring. However, the serum did help acne flare-ups dissipate more quickly after our tester added this product to their acne-prone routine. If you try to avoid oil-based products, though, this one might not be for you. Size: 1 oz. | Key Ingredients: Vitamin C (tetrahexyldecyl ascorbate), 15 super-greens complex, and pomegranate stem cells | Skin Type: All Best Smoothing Drunk Elephant C-Firma Fresh Vitamin C Day Serum PHOTO: Amazon $86 at Amazon $79 at Sephora $79 at Ulta Star Qualities Gave us softer, plumper skin and reduced breakouts Maintains nearly 95 percent of active vitamin C for one year after mixing Noticeably brighter and smoother skin after one month of use Red Flags Strong vitamin C concentration may be too strong for new users This OG serum is still holding up to its hype. The brand's proprietary C-Firma is designed to be mixed by you before its first use. This helps maximize potency; each bottle is proven to maintain almost 95 percent efficacy up to one year after mixing. After six weeks our skin was softer, plumper, and more luminous, and our monthly chin breakouts were significantly reduced. One of our testers even started receiving compliments on her skin, and after just three to four weeks of use, started to notice a visible difference in her complexion's brightness and texture. However, this Drunk Elephant serum has a 15 percent vitamin C concentration, so if you're just starting out with a vitamin C step in your skincare routine, it's better to start with a lower dose (around 10 percent concentration). Also, one of our testers noted an odd smell upon application but said it quickly faded. Size: 1 oz. | Key Ingredients: Vitamin C (15% L-ascorbic acid), ferulic acid, vitamin E | Skin Type: All PHOTO: People / Julia Sayers Gokhale PHOTO: People / Julia Sayers Gokhale PHOTO: People / Julia Sayers Gokhale Best for Dull Skin Biossance Squalane + Vitamin C Rose Oil PHOTO: Sephora $74 at Amazon $74 $40 at Sephora $14 at Walmart Star Qualities Absorbed quickly and didn't leave behind a greasy residue Compatible with a variety of skin types Its plumping effect gave our skin a much-needed refresh Red Flags On the pricier end Vitamin C percentage is not listed Applying face oil might feel like it goes against everything you learned about skincare. However, squalane soaks right into the skin and is usually well tolerated by most skin types, including oily and combination skin. In testing, we found that even testers with naturally oily skin loved this product, saying that the oil absorbed surprisingly well and never felt greasy post-application. The glow of this serum is excellent at combating dull skin, and one of our testers said she'd received so many compliments on her skin since incorporating this product into her daily routine. It also made her skin extra plump, as if she'd just gotten a great night's sleep. This product is on the more expensive side, but a little goes a long way, so we think it's worth it. Size: 1.01 oz. | Key Ingredients: Damascus rose oil, vitamin C, and Chios crystal oil | Skin Type: All People / Madison Yauger Best Exfoliating Ole Henriksen Banana Bright Vitamin C Serum PHOTO: Sephora $68 at Sephora $68 at Ulta View on Olehenriksen.com Star Qualities Made with hyaluronic acid Offers gentle exfoliation Improved skin elasticity and evened skin tone over time Red Flags Higher concentration of vitamin C may irritate those with sensitive skin With this 15 percent vitamin C-infused serum, you won't need to layer hyaluronic acid because it's already in this formula, which is a plus if you're an impatient skincare applicator. This serum has such a hydrating effect that our tester made it through a full day of Zoom calls and still looked dewy. It made our skin glowy, hydrated, and refreshed, and we loved the slight scent. It has a 15 percent vitamin C concentration, so if you're new to vitamin C or have sensitive skin, you may want to opt for a product with a 10 percent concentration. Size: 1 oz. | Key Ingredients: 15% vitamin C (ethyl ascorbic acid), PHAs, and hyaluronic acid | Skin Type: All People / Ivy Ford Add to Cart While you're adding vitamin C serum to your cart, round out your skincare routine with some of our other PEOPLE-Tested skincare winners that breezed through our rigorous testing with flying colors. Isdin Isdinceutics Hyaluronic Concentrate $115 at Amazon $115 at Dermstore $109 at Isdin.com ISDIN K-Ox Eye Cream $106 at Amazon $106 at Dermstore View on Isdin.com LilyAna Naturals Retinol Cream Moisturizer $24 at Target $26 at Walmart $30 at Lilyananaturals.com PanOxyl Acne Foaming Wash $10 at Amazon $10 at Target $10 at Walmart What to Know About Vitamin C Serum Yes, you can use it with retinol products. If your skin is not sensitive, you can apply both vitamin C and retinol at night. "If I'm going to use either retinol or vitamin C, I'll take retinol," Chung shares. This pairing can be a dynamic duo that gets you a little more bang for your buck if your skin isn't prone to irritation. "Retinol is your gold standard for increasing collagen and improving the turnover of skin cells while Vitamin C acts as a supporting cast," she explains. Prone to irritation? No problem. Instead, stick with vitamin C for the daytime and a retinol formula at night. Opt for a low concentration if you have sensitive skin. Most everyone can benefit from layering vitamin C into their routine, whether it be vitamin C serum or in an eye cream for dark circles. But if your skin is reactive or sensitive, Chung says to avoid high-concentration formulas that may cause irritation. Some vitamin C products are formulated specifically for sensitive skin, like SkinCeuticals C E Ferulic. If you have dry skin, try Sephora Collection’s Ultra Glow Serum, our top pick for dry skin. Look for dark or opaque packaging. Vitamin C serum that is packaged in a dark glass bottle or opaque plastic tube will last longer than one stored in clear packaging. It’s also important to store your vitamin C serum in a cool, dark place to avoid UV exposure, which can make it less effective. The Klur Brilliant Light Multi-Correctional Repair Serum, which is in a dark glass bottle, and our best overall, L'Oreal Paris Revitalift Vitamin C Serum, in an opaque tube, are examples of the ideal packaging for vitamin C serums. Consider the other ingredients. Vitamin C is usually thoughtfully formulated with complementary ingredients. The reason for this? "Vitamin C products often need oiler vehicles to maintain stability," Chung tells PEOPLE. However, she notes this can be problematic for some skin types (like acne-prone skin). So if you are prone to acne, seek formulas with squalane and rosehip oils, as they are non-comedogenic. Vitamin C can also be quite effective in hyaluronic acid serums and can be used in conjunction with niacinamide products. As far as the actual vitamin C goes, Chung recommends products that use L-ascorbic acid as its active ingredient, preferably with vitamin E, for the best stability. This is because L-ascorbic acid is the most potent and effective form of vitamin C. Our best daytime serum, Drunk Elephant C-Firma Fresh Vitamin C Day Serum, contains both L-ascorbic acid and vitamin E. Our tester applying Yes to Grapefruit Daily Brightening Serum. People / Allison Vancura Behind the Scenes To find the best vitamin C serums on the market, we gathered top-rated products and our team used them over a period of six weeks. We tested 32 vitamin C serums altogether on a variety of different skin types. All in all, we selected 14 vitamin C serums we feel confident would work well for a variety of people. Ease of Use: One of the biggest factors we considered was how easy it was to apply and layer the products with the rest of our normal skincare routines. We noted how well each dropper distributed the serum and if the bottle felt high-quality or breakable.Absorption: The next step was distribution, where we analyzed whether or not the serum absorbed quickly (in under 15 seconds) or took more than a minute to sink in, which would earn a poorer rating.Skin Texture: A major change we looked for when using these products was an improvement in our skin texture. We took photos to document our progress and noted any changes, no matter how big or small, in the smoothness and softness of our skin after the six-week testing period had passed.Glow: Vitamin C is supposed to brighten your skin, so we watched closely to see if our complexions boasted an extra glow after a few weeks of proper testing. We kept tabs on any extra dewiness and luminosity that appeared (or didn't) and rated each accordingly (more glow equals a higher rating).Firming: Another factor we took into consideration was the tightness of our skin after the testing period ended. Extra points if we noticed a reduced appearance of wrinkles as a result of these products.Overall Look: In general, we judged the overall look of our skin based on the luminosity of our complexions, the tautness of our skin, and if our dark spots and/or acne had faded since our first time using the serums.Value: The final step was analyzing the retail price, which was only revealed to us once the test was complete. After learning the amounts, we asked ourselves if we thought the price was worth it (or better yet, if we would have paid even more for the amazing results it delivered) and rated the quality based on our answers. Frequently Asked Questions How should I use vitamin C serum? There is one must when using vitamin C (and caring for your skin in general): SPF. "I recommend using vitamin C every morning before sunscreen," Los Angeles-based celebrity esthetician Shani Darden tells PEOPLE. "The combo of vitamin C serum and sunscreen is perfect for daytime protection." How often should I use vitamin C? Darden says a slow start is best if you're starting a vitamin C serum for the first time or adding a new vitamin C serum you haven't used before. Begin by using a small amount once a day, three or four days a week, and work your way up to a daily application."Vitamin C is a very active ingredient and it can cause irritation," she explains. "Introducing it slowly will allow time for your skin to acclimate to the product without causing any irritation. Additionally, adding the product in slowly and by itself will make it easier to pinpoint how well it works for your skin." When should I apply vitamin C serum? The best time to apply vitamin C serum depends on what other beauty products you’re using as well as your skin sensitivity level. Learning how to layer products and when to use them is a science, but once you get your routine down, it’s super simple. Chung encourages her patients with sensitive skin to use vitamin C serum in the morning, but you can also apply it at night with retinol. If your skin isn’t prone to sensitivity, the combination of vitamin C and retinol may give you faster results. If you are susceptible to irritation, use a vitamin C serum in the morning and a retinol at night. Why Trust PEOPLE? Bianca Lambert is a freelance writer for PEOPLE and is also a contributing writer for Byrdie, specializing in natural hair and skincare. She has worked as a freelance beauty writer for over four years and has an extensive knowledge of beauty ingredients and how they affect your skin, hair, and face. For this article, she consulted our testing results and interviewed board-certified dermatologists and celebrity estheticians to provide real-world experience and expert guidance on the topic at hand. This article was most recently updated by PEOPLE shopping writer Cai Cramer, with updated insights and fresh picks. Meet Our Experts • Dr. Christina Lee Chung is a board-certified dermatologist at Schweiger Dermatology Group in Pennsylvania. • Shani Darden is a Los Angeles-based celebrity esthetician and founder of Shani Darden Skin Care. What Is People Tested? We created the PEOPLE Tested seal of approval to help you find the very best products for your life. We use our unique methodology to test products in three labs across the country and with our network of home testers to determine their effectiveness, durability, ease of use, and so much more. Based on the results, we rate and recommend products so you can find the right one for your needs. But we don’t stop there: We also regularly re-review the categories in which we’ve awarded the PEOPLE Tested seal of approval — because the best product of today might not be the best of tomorrow. And by the way, companies can never buy our recommendation: Their products must earn it, fair and square. In short, PEOPLE Tested provides recommendations you can trust — every day, every purchase.