If you're seeking a brighter, more even complexion (and aren't we all?), then two of the best active ingredients to try are vitamin C and acids.
Both are well-known for giving skin a glow—but fitting them into your skincare routine is where it gets tricky.
Do they have to be applied at different times, or can you use them together? Will one inactivate the other? Which one goes on first? What about wait times?
This tutorial is going to answer all those questions for you, and more. You will learn:
- What vitamin C and acids can do for your skin
- The best ways to incorporate them into your routine
- Which ingredient to apply first and how long to wait in between layers
- Why pH matters, and the pH levels of my recommended products
I've also got a free cheat sheet for you to download at the end of this article!
The Benefits of Vitamin C and Acids for Your Skin
Before we talk about how to apply them, here's why you'd want to use both a vitamin C serum and an acid in the first place.
Vitamin C is a powerful antioxidant, so it protects your skin from premature aging by neutralizing free radicals. It also helps to repair existing damage by normalizing collagen production and blocking excess melanin formation—which means your skin will become firmer, more even-toned and more radiant.
There are two types of vitamin C:
- L-ascorbic acid is the active form of vitamin C, and the most potent. The downside is that it is quick to oxidize in the presence of heat, light and air.
- Vitamin C derivatives—such as sodium ascorbyl phosphate, ascorbyl glucoside and ethyl ascorbic acid—need to be converted into active vitamin C within the skin. While that makes them milder than L-ascorbic acid, they tend to be more stable.
Acids are chemical exfoliants that loosen and peel away dead skin cells. This gives an immediate brightening effect, since dead cell build-up absorbs light instead of reflecting it. Over time, acids also help to remove dark spots, reduce fine lines and acne, and even increase firmness.
There are two main types of acids:
- AHAs (alpha-hydroxy acids) exfoliate the surface layer of the skin. Glycolic acid and lactic acid are the most common and effective AHAs.
- BHAs (beta-hydroxy acids) exfoliate the skin surface as well as deep inside the pores. Salicylic acid is the most common and strongest BHA, while betaine salicylate is an increasingly popular gentle alternative.
Both vitamin C and acids are superior ingredients for addressing dullness and discolourations, but they work differently. So pairing them together can give you better results versus using either one on its own.
The only catch? You need to apply your products at the right time, in the right order.
How to Use Vitamin C and Acids in Your Skincare Routine
Option 1: Apply Them at Different Times of Day
The simplest way to incorporate vitamin C and acids in your routine is to apply them away from each other, at different times of day.
This is a good approach for beginners and sensitive types, since AHAs, BHAs and L-ascorbic acid are all acidic ingredients. By separating them, you're less likely to irritate your skin.
As for which active you put on when, it's up to you.
In the past, most dermatologists have recommended using vitamin C serums in the morning. Dr. Neal Schultz, however, believes that a nighttime application is even more beneficial. Away from UV light, the vitamin C "gets fully absorbed into your cells where it's really needed," he told Vogue.
Acids can also be used at any time, as long as you're protecting your skin with a good sunscreen during the day. BHAs have some photoprotective properties, so they're ideal for mornings, while AHAs make your skin more sun-sensitive, so they're your best bet at bedtime.
Option 2: Apply Them on Alternate Mornings or Nights
Another easy option is to alternate between a vitamin C serum and an acid at the same time of day. So, for example, one morning you could apply your L-ascorbic acid, and the next morning, your favourite BHA.
An advantage of this approach is that you're taking it slow, so your skin will be able to gradually adjust to the two active ingredients. It's also a good idea if you have sensitive skin and can't tolerate using acid exfoliants on a daily basis.
But is it enough to be effective? According to celebrity facialist Kate Somerville, yes. "I've seen some amazing results with clients who've added vitamin C into their regimen at three times a week and worked up to daily use," she told Vogue.
Option 3: Apply Them at the Same Time
You might be surprised to know that it's also possible to apply your vitamin C serum and acid together, at the same time.
In fact, using an acid right before vitamin C could actually ENHANCE your results.
We know that AHAs and BHAs—which are typically between pH 3.0 and 4.0—make the skin more acidic by lowering its pH. So by applying an acid first, it will create the optimal conditions for the L-ascorbic acid to be effective.
Acids may even improve the conversion of vitamin C derivatives into L-ascorbic acid.
"Non-acidic forms of vitamin C are almost always of a higher pH than AHAs, so be sure that you acidify the skin first so that the THD [tetrahexyldecyl ascorbate], MAP [magnesium ascorbyl phosphate], or ascorbyl glucoside (AG) can actually be broken down or transformed/activated into L-ascorbic acid to begin with," suggests FutureDerm founder Nicki Zevola Benvenuti.
Option 4: Apply Them 30 Minutes Apart
Your final alternative is to apply your vitamin C serum and acid 30 minutes apart.
Personally, I always take this approach whenever I'm using products that have a gap of more than about 1.0 to 2.0 in pH levels.
So while I wouldn't wait in between an AHA and L-ascorbic acid, for example, I'd do so with a higher-pH vitamin C derivative, such as:
- Ascorbyl glucoside: pH 5.0-7.0
- Ascorbyl tetraisopalmitate: pH 4.0-6.0
- Ethyl ascorbic acid: pH 4.0-5.5
- Magnesium ascorbyl phosphate: pH 6.0-7.0
- Sodium ascorbyl phosphate: pH 6.0-7.0
The same goes for vitamin C formulas that are anhydrous (water-free), which don't have a pH level at all.
But wait—didn't I just mention that acidifying the skin could enhance the conversion of vitamin C derivatives into active vitamin C?
Yes, but here's something else to consider. If you layer one right on top of the other, the vitamin C derivative (or anhydrous L-ascorbic acid) is likely to dilute or raise the pH of the acid—which would reduce its effectiveness. This study looked at the absorption of AHAs at pH 3.0 versus pH 7.0, and found that the higher the pH, the less the skin absorbs.
In other words, if getting the most out of your acid exfoliant is important to you, incorporate a waiting period to give it time to work, before applying your vitamin C derivative on top.
Recommended Vitamin C Serums and Acids (and Their pH Levels)
So let's finish with a few product examples, shall we?
Here are a few of my favourite vitamin C serums and acid exfoliants, in a range of strengths—and how I'd pair them together based on pH levels.
Lotion P50 + C E Ferulic
As any skincare aficionado knows, these are two of the most coveted and high-quality formulations for maximum results. The acid has 12.85 percent AHAs, while the vitamin C serum has 15 percent L-ascorbic acid. No waiting period is required.
Skin Perfecting 2% BHA Liquid Exfoliant + C-Firma Day Serum
This is one of the stronger BHA treatments on the market, with two percent salicylic acid to clear and prevent breakouts. As such, it's a good match for this 15 percent L-ascorbic acid serum infused with marula oil. And you don't need to wait in between them.
- Paula's Choice Skin Perfecting 2% BHA Liquid Exfoliant: pH 3.2-3.8
- Drunk Elephant C-Firma Day Serum: pH 3.3
Knockout Tingling Treatment + C15 Super Booster
This toner with a 10 percent AHA and BHA blend will prep your skin to receive the 15 percent L-ascorbic acid serum. Again, since they are close in pH, no waiting period is necessary.
Lactic Acid 10% + HA + Ascorbyl Glucoside Solution 12%
For sensitive skin, this 10 percent lactic acid and 12 percent ascorbyl glucoside (a vitamin C derivative) are a good match. Due to the gap in pH levels, space them out at least 30 minutes apart.
- The Ordinary Lactic Acid 10% + HA: pH 3.6-3.8
- The Ordinary Ascorbyl Glucoside Solution 12%: pH 6.0-7.0
BHA Blackhead Power Liquid + Vitamin C Serum
This four percent betaine salicylate treatment is unusual in that it has a higher pH than most acids, but as per my review, that doesn't diminish its effectiveness. I'd wait 30 minutes before layering the sodium ascorbyl phosphate formula (a vitamin C derivative) on top.
AHA 7 Whitehead Power Liquid + Ethylated Ascorbic Acid 15% Solution
Here's another acid with a slightly higher pH level, and seven percent glycolic acid. That makes it less irritating than other glycolic acid formulas. Leave it on 30 minutes before you put on the vitamin C derivative, ethyl ascorbic acid. (Since the latter is anhydrous or water-free, you don't want to apply it too soon and dilute the acid.)
- COSRX AHA 7 Whitehead Power Liquid: pH 4.0-5.0
- The Ordinary Ethylated Ascorbic Acid 15% Solution: Water-free
Conclusion + Free Cheat Sheet
Now you know how to use vitamin C serum and an AHA or BHA in your skincare routine.
The idea that acids inactivate or destabilize vitamin C seems to be one of those things that gets repeated all the time, but isn't exactly true. As I've shown you here, acids and vitamin C can actually be very compatible!
You just need to know the pH of your products to decide whether or not to incorporate the 30-minute waiting period.
That's why I created the Types of Vitamin C Cheat Sheet. Just click below to download it so you have a guide to all the different forms of vitamin C, including pH levels, and how they benefit your skin. (It's FREE!)
Of course, if you want to take a slower, gentler approach—or if you can't be bothered worrying about this whole pH business—feel free to simplify your life and apply these ingredients at different times of day or on alternate days.
And remember, results take time. While you should start seeing the brightening benefits from your acid within mere days, it can take at least a month or two for dark spots to start fading. The same goes for vitamin C, which needs to be used regularly for at least a couple months to tackle stubborn pigmentation.
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Does your routine include both a vitamin C serum and an acid?
How do you prefer to apply them?