Experts Say You're Wasting Your Money on Vitamin C Unless You Know This One Thing

Of all the skincare ingredients I love (niacinamide to treat fine lines, peptides for plumper skin, retinoids… need I go on?), vitamin C might be the one I love the most. That's for two reasons: The first is that it's a true multitasker and has myriad benefits. (More on that in a minute.) The second is that it's made a big difference in the state of my skin. Over time, it's made my skin look brighter and more even toned.

That doesn't mean I'll use any old vitamin C product that comes my way. In fact, it's quite the opposite. I'm very picky about the whole thing, and I only hold a few vitamin C products in high enough esteem to give them a spot on my bathroom counter. It's not that I'm being finicky; it's that choosing the right one matters. Using it correctly matters too. Ahead, discover everything you need to know before using vitamin C—straight from an aesthetician.

The Benefits of Vitamin C

First, let's talk about the benefits of vitamin C and how it functions in the skin. According to SkinSpirit lead aesthetician Karen Fernandez, "vitamin C is an antioxidant that helps reduce environmental damage."

In other words, it fights those pesky unpaired electrons that we call free radicals. If you didn't know, free radicals come from all sorts of different things, including sun exposure, pollution, and even normal metabolic processes in the body. They can damage DNA and lead to signs of aging, like fine lines and wrinkles. The antioxidant function of vitamin C prevents that from happening. "It surrounds the skin cells and deflects triggers that want to harm your skin," Fernandez says. "I think of vitamin C as 'your internal SPF' designed to protect and embedded in your epidermal skin layer."

The best part is that vitamin C does double duty. It's an antioxidant, and it also functions as a skin brightener. Over time, vitamin C can brighten dullness and lighten dark spots and hyperpigmentation. In other words, it can give you a more even-toned complexion.

It works for all skin types, regardless of how dry or oily you are or what concern you're trying to tackle. That goes for all antioxidants. "Antioxidants are good for all skin and skin types," Fernandez says. "They prevent damage and also visibly brighten skin."

Are there any potential downsides?

While vitamin C is unrivaled as a skin-brightening antioxidant, there is a catch, and that's that it's notoriously unstable. If it breaks down (or oxidizes) before it hits your skin, it'll be rendered ineffective. What's more, the oxidized vitamin C could potentially cause irritation and blackheads.

"That is the downside of vitamin C," Fernandez says. "It can be unstable, which means it can be made ineffective by environmental factors, like too much light or heat. For most formulas, the color will darken, and it will have an incorrect balance of actives and alcohol."

How do you make sure your vitamin C is stable? Fernandez says all you need to do is check the color and smell of the product. If the color is darker than it was when you bought it (for example, if it turned a dark brown) or it smells a little funky, toss it. It's not worth using anymore. It's already oxidized, and you simply won't be getting the benefits you once were. To prevent this from happening, Fernandez recommends making "sure to store in a temperate place with no direct sunlight or heat fluctuations."

How to Use Vitamin C

Fernandez recommends using vitamin C daily and in the morning under sunscreen. "It is designed to protect your skin and can do that all day," she says. Just know antioxidants can benefit the skin both morning and night, which is why she also recommends incorporating an antioxidant serum into your nighttime routine. "Some antioxidants have reparative aspects and will regenerate the skin's cells at night while you sleep," she says. "This rebuilds and replenishes cells from the inside out, leaving skin refreshed in the morning and able to defend against the day's aggressors."

The only time you shouldn't use vitamin C is when your skin is sensitized from an in-office treatment. While Fernandez says there are formulas out there that are designed to help the healing process and can be good for post-treatment skin, the majority are not: "Unfortunately, most over-the-counter vitamin Cs are not medically formulated and will just irritate skin that is already sensitized."

What shouldn't you mix with vitamin C?

While some antioxidants (like vitamin E and ferulic acid) can supercharge vitamin C's benefits, other players don't interact too well with the ingredient. See below for a few callouts.

• AHAs and BHAs: AHAs (think glycolic acid, lactic acid, mandelic acid, etc.) and BHAs (like salicylic acid) are intense skin exfoliators. When combined with potent vitamin C, it can lead to irritation.
• Retinol: Similarly, retinol is generally a very potent, unstable active—and so is vitamin C. Having the two active ingredients competing for the same real estate is a recipe for irritation and skin barrier damage.
• Benzoyl Peroxide: Benzoyl peroxide (you know, that acne-clearing hero!) is an oxidizer, which means it can render vitamin C ineffective. Vitamin C naturally oxidizes over time as it becomes exposed to light and air, so you definitely don't want to speed up the degradation!
• Niacinamide: This one's a little tricky. Some people report flushing and inflammation when using niacinamide and vitamin C in the same routine. Others fare totally fine. If you have a preformulated product that combines both ingredients, you're probably A-okay since those formulas are likely already tested for compatibility. If you have stand-alone vitamin C and niacinamide serums, though, you might want to proceed with caution—especially if you have sensitive skin.

Is vitamin C good for your face every day?

In short, yes! Fernandez recommends incorporating antioxidants into your routine twice a day—morning and night—and vitamin C is a solid choice. If you're new to vitamin C, perhaps start slow with a few days per week and work your way up to a daily cadence, noting any potential irritation.

The Best Vitamin C Products, at a Glance

• Best Overall: SkinBetter Science Alto Advanced Defense and Repair Serum
• Best for Acne-Prone Skin: Revision Skincare C+ Correcting Complex 30%
• Best With Vitamin E: SkinCeuticals C E Ferulic
• Best for Mature Skin: IS Clinical Super Serum Advance Plus
• Best Budget: Naturium Vitamin C Super Serum Plus

Shop 10 Effective Vitamin C Products 

We have a full guide to vitamin C serums for you to browse, but feel free to check out some standouts below.

Best Overall: SkinBetter Science Alto Advanced Defense and Repair Serum

Best for Acne-Prone Skin: Revision Skincare C+ Correcting Complex 30%

Best With Vitamin E: SkinCeuticals C E Ferulic

Best Vitamin C Moisturizer: Laneige Radian-C Cream With Vitamin C

Best for Sensitive Skin: Renée Rouleau Vitamin C&E Treatment

Best for Mature Skin: IS Clinical Super Serum Advance Plus

Best Vitamin C Face Oil: Sunday Riley C.E.O. Glow Vitamin C + Turmeric Face Oil

Best Multitasker: Paula's Choice C15 Super Booster

Best Budget: Naturium Vitamin C Super Serum Plus

Best Drugstore: La Roche-Posay 10% Pure Vitamin C Anti-Aging Face Serum

This article was originally published at an earlier date and has been updated.