This K-beauty favorite serum contains a mild dose of 5 percent vitamin C to allow your skin to accustom itself with the active ingredient. While that's still enough to notice the brightening and skin tone-evening benefits, the smaller percentage means its also gentler and less likely to irritate skin. Reviewers love its lightweight texture and say a little goes a long way, so you only need a couple of drops. Some have even had luck with using it on their bodies to help fade unwanted scars.

Klairs Freshly Juiced Vitamin C Serum is also an Amazon-user favorite with hundreds of five-star reviews. "I used this product for a few months and then switched to one with a higher percentage of Vitamin C only to find that it didn't work nearly as well," writes one reviewer. "I'm back to using Klairs and am so impressed by the positive change I see in my skin when I use it — it's brighter, smoother, and more even — even though it's a mild product."

The only downside with this serum is that, since it comes in a clear bottle, you'll want to be extra careful with storing it somewhere away from the sun.

If you have sensitive skin, you might have luck with the low-concentration Klairs option, above. But it does contain a few ingredients that some particularly sensitive skin types negatively react to, like propylene glycol. For a super safe, all natural pick, try this all-natural pick from Mad Hippie. It uses vitamin C in the form of sodium ascorbyl phosphate, which is said to cause less irritation and reduce the risk of oxidation. Mad Hippie formulated this serum with other complementary ingredients, like vitamin E and ferulic acid, which both improve and protect the skin from damaging free radicals. And ferulic acid also helps stabilize both vitamins C and E, so that they're even more effective. To keep skin moisturized, hyaluronic acid is included in the formula, while konjac root and chamomile extract work to protect and soothe the skin. There's also a dose of clary sage, which acts as a natural toner and astringent.

"I have very sensitive skin and normally I cannot use vitamin C serums at all," writes a reviewer. "This one does not sting or burn at all." Another user notes, "Within a week or so, I saw a smoother texture to my skin. By the end of the bottle, my skin looked smoother, brighter, and three darker spots on my face [from sun damage] were at least 80 percent lighter."

Yes, all vitamin C serums brighten the skin with continued use, but The Body Shop Vitamin C Skin Boost Instant Smoother also leaves skin glowing directly after you apply it, thanks to the tiny mineral glowing particles it contains. Long-term brightening, protecting, and collagen-boosting effects come from ascorbic acid and the vitamin C-packed camu camu berries that The Body Shop has hand harvested by local collectors on the riverbanks of the Amazon River. Vitamin E provides the skin with more protection against environmental aggressors as it softens, and Community Fair Trade Brazil nut oil further moisturizes the skin. Additionally, dimethicone and glycerin give the serum a smooth texture that helps to blur pores and even out skin tone, making this a great primer, too.

This serum might be a bit of a splurge, but its powerful formula means serious results. The brand works with a team of assorted experts to develop each product, including geneticists, biologists, and physicians. For their iS Clinical Pro-Heal Serum Advance+, they developed a vitamin C combo that works for all skin types, including acne-prone. Time-released vitamin C means prolonged antioxidant protection, while vitamins E and A contribute even more antioxidant benefits. iS Clinical included inflammation-reducing zinc sulfate, blemish-preventing kojic acid, and nourishing olive leaf extract to combat signs of acne while helping to prevent future breakouts.

For a more affordable option, e.l.f's Beauty Shield Vitamin C Pollution Prevention Serum costs less than $20. Despite its low price, the serum still contains your vitamin C, as well as vitamin E and pomegranate extract, which provides even more vitamin C benefits. You'll also notice glycerin and hyaluronic acid on the ingredients list to leave the skin smooth and moisturized. It's even cruelty-free and vegan, and formulated without parabens, sulfates, or phthalates.

If you're into DIY beauty (or you just want to customize your vitamin C application), a vitamin C booster powder, like the Resurrection Beauty L-Ascorbic Acid Powder, is the perfect choice. This jar solely contains vitamin C in the form of l-ascorbic acid, which is meant to be dissolved in water or witch hazel before being added into your favorite hydrating serum. It can even be added to your nightly moisturizer, sunscreen, or body lotion. Because you're mixing this yourself, you can start with a lower concentration of vitamin C, like 5 percent, and work your way up to 20 percent (the maximum amount recommended) as your skin learns to tolerate it.

Many Amazon reviewers share the different ways they use this powder to make custom treatments. "How terrific to find cosmetic grade vitamin C to make my own solution," one raves. "All skin care experts claim this is the best for anti-aging, however very unstable. This fixes the problem and at an reasonable price. I just mix small batches to last for a week. And in just a few weeks I can see the difference in my skin." Another recommends mixing it with aloe-vera for a skin-soothing and brightening mask.

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