The Expert’s Guide To Using Vitamin C

Along with SPF, retinol and a gentle cleanser, dermatologists and other skin experts often tout vitamin C as one of the most beneficial ingredients to add to a simple, everyday skin-care routine.
While the popular antioxidant stars in numerous face masks, toners, mists, and moisturizers, the most efficient way to deliver it straight into your skin for best results tends to be with a potent, targeted serum. Just like retinol, though, vitamin C can be quite tricky to master, as it's an unstable ingredient and prone to change when exposed to light and air.
With dermatologists and skin specialists recommending vitamin C more than ever, here's everything you need to know about the buzzy molecule, including why you should start using it ASAP.
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What is vitamin C?

Otherwise known as ascorbic acid, vitamin C is found in food and supplements, and also has proven skin-care benefits when applied topically to the skin.

What does vitamin C do for skin?

"Vitamin C is essential," says Christopher Corinthian, development chemist for Avon. "It’s a powerful antioxidant that fights against free radicals that cause aging," such as pollution. As Nicolas Travis, skin expert and founder of skin-care brand Allies of Skin, explains, these environmental "nasties" cause inflammation, which is believed to be at the root of numerous skin issues, including breakouts, a breakdown of collagen, and excess melanin production that leads to dark spots.
Vitamin C is also a known brightener, and using it regularly has the ability to even out skin tone. "Vitamin C can reduce dark spots by minimizing the formation of excess melanin in the skin," Travis says. "This helps promote radiance when used daily." The ingredient can also stimulate collagen production. "Collagen production depletes as we age," Travis says. "Vitamin C helps your skin repair damaged cells, maintaining what we have for fresher-looking skin."

How should you use vitamin C?

Travis says that a serum is the preferred form of vitamin C. "They usually contain the ideal delivery system, and are designed to be used before moisturizer," he explains.
While vitamin C can be used in the morning or evening, most prefer to apply it during the day since its antioxidant properties act as a shield to deflect pollution and other environmental aggressors. In terms of when you should use it in your routine, Corinthian suggests a three-step system of cleansing, treating, and moisturizing. That second step would be vitamin C application, followed by moisturizer, unless you have oilier skin and prefer to use a serum on its own.
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Which vitamin C is best?

"Though products say vitamin C on the front, you can only determine if that is pure vitamin C by looking at the label on the back," Corinthian says. "The Avon Anew Vitamin C Brightening Serum includes 10% pure vitamin C, otherwise known as ascorbic acid. Some products that claim to include vitamin C might only include a vitamin C derivative, for instance, ascorbyl palmitate. With these forms, you're not getting the same protection as you would if you were to use pure vitamin C." For a potent concentration of ascorbic acid at a lower price, The Ordinary's Ethylated Ascorbic Acid 15% Solution is a fan favourite.

How can you get the most out of your vitamin C?

Both Corinthian and Travis suggest teaming vitamin C with SPF for bolstered protection against the environment, as sunscreen absorbs UVA and UVB rays. "Using both daily has been proven to reduce signs of premature aging," Travis says.

Which ingredients should you avoid when using vitamin C?

To avoid irritation, Travis suggests skipping any exfoliating acids immediately after applying vitamin C. "You can absolutely use them in the same regimen, just not at the same time," he says. "Use vitamin C in the morning every day, and exfoliating acids in the evening on an alternate basis."
London-based cosmetic doctor Dr. Paris Acharya recommends avoiding buzzworthy skin-care ingredient niacinamide when using vitamin C. "Niacinamide inactivates vitamin C if it is in a combined water-based product," Dr. Acharya says. That doesn't mean you have to avoid it altogether: If you want to use niacinamide, just do so as part of a nighttime routine.
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How do you know if your vitamin C serum is working?

Corinthian says that if your vitamin C serum changes colour, it might be time to throw it away. "When vitamin C is exposed to air, it oxidizes and changes its form into something that isn’t as effective, and it doesn’t work as well on your skin," he explains. "When the oxidation happens in a product, it goes from a lively golden colour to more of an orange-brown colour. That’s your visual clue that you might not be getting all of the vitamin C the product says you’re getting." If anything, Corinthian says you’re probably getting more moisture from other ingredients built into the serum base than the actual vitamin C itself.
It also pays to look out for the type of packaging your vitamin C serum is in. "Vitamin C products in tinted or coloured glass typically mean they're not stable," Corinthian says. "When you expose vitamin C to air, you are exposing it to accelerating being oxidized." Opt for a product in an airtight pump rather than a dropper bottle, for example, as it'll last longer and be more effective.

Does vitamin C cause skin reactions?

"L-ascorbic acid, a very common form used in vitamin C products, has to be formulated at a low acidic pH, usually 3 to 3.5, which makes it as acidic as over-the-counter chemical peels," Travis says. "This is why you might experience a tingle or itching sensation."
Corinthian acknowledges that some people are more sensitive to certain ingredients. "I would lower the frequency at which you use the vitamin C product until your skin acclimates," he says. Contrary to popular belief, the tingling or itching sensation doesn’t mean dehydration at all. "It's more likely just sensitivity. Just space it out until you feel comfortable using it."
This story was originally published on Refinery29 UK.
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