Frequently asked questions
What is vitamin C, and what does it do?
Vitamin C is an antioxidant, and our bodies need it to function properly. You might associate it with citrus fruits like oranges, lemons, kiwis, and grapefruit, but its health perks extend to your skin, too.
When ultraviolet light penetrates your skin, it causes lasting damage by producing free radicals. Vitamin C can prevent that damage by neutralizing the free radicals before they form, says Kenneth Howe, MD, a board-certified dermatologist in New York City. The brightening serum also inhibits a key enzyme in melanin production, so it can act as a dark-spot corrector too. The result: A more radiant complexion and smoother texture over time. (Think glass-like skin.)
“Vitamin C also helps defend against free radical damage caused by environmental stressors like UV exposure and pollution,” says Corey L. Hartman, MD, a board-certified dermatologist and founder of Skin Wellness Dermatology in Birmingham, Alabama. “Vitamin C aids in reducing hyperpigmentation and dark spots caused by acne scarring or sun exposure. Research has also shown that vitamin C helps stimulate collagen production, which makes skin appear firmer and reduces the appearance of fine lines and wrinkles.”
What to look for in a vitamin C serum
The key ingredient in these serums is L-ascorbic acid, a pure form of vitamin C, says Joshua Zeichner, MD, a board-certified dermatologist in New York City. This type of vitamin C penetrates more deeply than other forms, making it more likely to reach the skin layers where you actually need it to work. Another form, Tetrahexyldecyl ascorbate, tends to be more stable than its counterparts (read: it lasts longer).
Pay attention to the concentration, too. “Look for serums that contain 10% to 20% vitamin C,” says Morgan Rabach, MD, a board-certified dermatologist in New York City. “Less than 10% is not as effective, and over 20% can cause skin irritation.” A supporting cast of active ingredients, such as vitamin E and ferulic acid, can also boost its efficacy. Some vitamin C serums may even boast nice-to-haves, including hyaluronic acid, squalane, and other hydrators.
Don’t forget to peep the packaging. Vitamin C is notoriously unstable and can oxidize in the presence of light and heat. You want darkly tinted glass bottles with airless delivery, since air can also cause pure vitamin C to degrade, says Dr. Rabach. That being said, it’s important to store your vitamin C serum in a cool, dark place.
Important to note: Vitamin C typically expires three to six months after opening. But always check the product label for specific guidelines, says Dr. Collins. “Vitamin C [ascorbic acid] is highly sensitive to light, air, and heat, which can lead to oxidation,” she explains. “Once oxidized, the serum turns a brownish or yellowish color and becomes less effective at delivering its skin-brightening and collagen-boosting benefits. Oxidized vitamin C may even cause skin irritation for some individuals.”
How to apply a vitamin C serum
Use vitamin C serum in the morning, once daily, followed by face sunscreen,”says Dr. Hartman. Because vitamin C is a powerful ingredient, it’s best to avoid layering with other strong actives like retinol. “Try your retinol during your evening skin care routine and a vitamin C product in your a.m. routine,” says Dr. Hartman. “Doing so will ensure you get the maximum benefit without risking irritation.”
Does vitamin C serum expire?
Yes, typically within three to six months after opening. But always check the product label for specific guidelines, says Dr. Collins. “Vitamin C [ascorbic acid] is highly sensitive to light, air, and heat, which can lead to oxidation,” she explains. “Once oxidized, the serum turns a brownish or yellowish color and becomes less effective at delivering its skin-brightening and collagen-boosting benefits. Oxidized vitamin C may even cause skin irritation for some individuals.”
What ingredients should you avoid mixing with vitamin C?
Avoid mixing them with retinol or AHAs like glycolic acid and lactic acid. “Most people use a vitamin C serum in their morning routine, so leave the retinol creams and AHAs for your evening skin care,” says Dr. Hartman.
Are vitamin C serums effective for dark spots and wrinkles?
Vitamin C serums can be effective for dark spots when combined with other ingredients like niacinamide or tranexamic acid, according to dermatologists. As far as wrinkles, vitamin C can stimulate collagen production, which can improve the appearance of fine lines over time. “It also protects against free radical damage from UV and pollution exposure, both of which contribute to premature aging,” Dr. Garshick adds.
What vitamin C serum is best for older skin?
If you have aging skin, dermatologists often recommend a potent antioxidant blend that supports brightening and collagen health. “Look for additional antioxidants in addition to vitamin C and E to help protect against free radical damage and environmental stressors, which can lead to signs of aging, including discoloration, fine lines and wrinkles, and collagen breakdown, while also helping to protect the skin against blue light and pollution,” says Dr. Garshick.
We started with about 25 of the most popular vitamin C products—all recommended by dermatologists and Glamour editors—and testers between the ages of 29 and 60. We then narrowed down this list to 15 total products based on their availability, ingredients, and derm recommendations, and had our editors rigorously test them over the past year. We evaluated everything from consistency to scent, plus monitored both short- and long-term results. We also tapped dermatologists for tips to understand how to get the most out of these serums. The best vitamin C serums met the following criteria:
| Ingredients | Format and Texture | Efficacy |
|---|---|---|
| Every serum included a variety of vitamin C types, including L-ascorbic acid, sodium ascorbyl phosphate, ethyl ascorbic acid, ascorbyl glucoside, and more. The best serums also contained other ingredients we rely on for bright, bouncy skin, such as ferulic acid, hyaluronic acid, niacinamide, and even polyhydroxy acids. | We paid close attention to how each serum felt on the skin: how lightweight it was, how quickly it sank in, and whether it left behind any stickiness or residue. None of the serums on this list were greasy or heavy, and all left our skin feeling soft and comfortable. | Finally, we asked: Did it actually work? The winners gave us long-lasting radiance and improved our discoloration and hyperpigmentation. They also addressed overall dullness, uneven skin tone, and texture. |
- Charlotte Birnbaum, MD, board-certified dermatologist at Spring Street Dermatology in New York City
- Kristina Collins, MD, board-certified dermatologist at Austin Skin in Austin
- Marisa Garshick, MD, board-certified dermatologist based in New York City, a board-certified dermatologist based in New York City
- Nava Greenfield, MD, board-certified dermatologist at Schweiger Dermatology in New York City
- Corey L. Hartman, MD, board-certified dermatologist and founder of Skin Wellness Dermatology in Birmingham, Alabama
- Kenneth Howe, MD, board-certified dermatologist in New York City
- Brooke Jeffy, MD, board-certified dermatologist in Arizona
- Morgan Rabach, MD, board-certified dermatologist in New York City
- Joshua Zeichner, MD, board-certified dermatologist in New York City
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