This article was last updated in December 2018.
If you're seeking a brighter, more even skin tone (and aren't we all?), then two of the best ingredients to try are acids and vitamin C.
Acids are great because they exfoliate away dull, dead skin and gently remove discolourations over time. AHAs (alpha-hydroxy acids) target the surface layers of the skin, while BHAs (beta-hydroxy acids) also unclog pores.
Then there's vitamin C, a powerful antioxidant that boosts radiance and helps fade sun damage.
You could use each one on its own, but if you want to really take your benefits to the next level? Consider including both in your routine!
That's where this tutorial comes in. You might be a little unsure of how to go about layering these actives. Do they have to be used at different times? Will one inactivate the other? Which one goes on first? What about wait times?
I've got answers! Keep reading to learn:
- The rationale for using acids and vitamin C separately
- How layering them together can actually give you even better results
- Which ingredient to apply first
- How long to wait in between layers
Option 1: Using Acids and Vitamin C at Different Times
If your skin is dry or sensitive, consider using acids and vitamin C at different times of day.
Why? Because AHAs, BHAs and vitamin C are all acidic ingredients, so there's more risk of exacerbating those conditions and irritating your skin.
So you could do:
- Vitamin C in the morning and an AHA or BHA at night
- AHA or BHA in the morning, and vitamin C at night (keeping in mind that AHAs make skin more sun-sensitive)
- AHA or BHA one night, vitamin C the next
"Do not use with exfoliating/filling high-concentrate vitamin C or A products, or other products with BHA and AHA. If you want faster effect, we recommend that you use one in mornings and other in evenings, or use them one at a time on each separate day."
But let's break this down a bit more. They do have a point with regards to vitamin A. We've already talked how acids can impair retinol conversion.
[Read more about how to use acids and retinol in a skincare routine]
So do acids need to be separated from vitamin C for the same reason?
Not always! In fact, acids and vitamin C can be VERY compatible...
Option 2: Layering Acids and Vitamin C Together
If your skin can tolerate them, it is possible to use acids at the same time as vitamin C.
That "acids destabilize vitamin C" seems to be one of those things that is repeated all the time, but isn't exactly true. I have not found any evidence that layering two pH-compatible products would render either one ineffective—in fact, quite the opposite!
Using an acid right before your vitamin C could actually ENHANCE your results. Here's why:
- Acids help prep the skin for better absorption of active ingredients, including vitamin C. By removing barrier-forming dead cells, you increase the rate of penetration.
- AHAs and BHAs make the skin more acidic (they lower pH).
- According to studies here and here, the active form of vitamin C, L-ascorbic acid, has been found to absorb best at a low pH.
In other words, an acid can create the optimal conditions for the vitamin C to be effective.
The catch? You need to know the pH of your products!
Acid or Vitamin C First?
Just like products should always be applied in order of thinnest to thickest, you also want to move in the direction of lowest to highest pH.
That means your most acidic product should go on first.
Usually, but not always, this will be your AHA or BHA. Here are the pHs of my most-recommended acids:
- COSRX BHA Blackhead Power Liquid: pH 4.0
- Biologique Recherche Lotion P50T and P50 PIGM 400: pH 3.5-4.0
- Paula's Choice Skin Perfecting 2% BHA Liquid: pH 3.2-3.8
- The Ordinary Salicylic Acid 2% Solution: pH 3.2-3.5
- The Ordinary Lactic Acid 10% + HA: pH 3.6-3.8
- The Ordinary Lactic Acid 5% + HA: pH 3.6-3.8
(If, for some reason, you wanted to use both an AHA and a BHA at the same time, the order wouldn't really matter if they are close in pH. If there's a bigger gap, apply the lower pH product first. Texture is important, too—you'd want to go in order of thinnest to thickest.)
Then would come your vitamin C. The first two are my current favourites:
- The Ordinary Ascorbyl Glucoside Solution 12%: pH 6.0-7.0
- Hylamide C25 Stabilized Vitamin C Booster: Not pH-dependent
- Mad Hippie Vitamin C Serum: pH 6.5-7.5
- NIOD Ethylated L-Ascorbic Acid 30% Network: Not pH-dependent
- The Ordinary Ethylated Ascorbic Acid 15% Solution: Not pH-dependent
The exception is if your acid has a thicker texture (like a cream), or if your vitamin C has the lower pH. In that case, apply the C first, then your acid. These are vitamin Cs with lower pHs:
- SkinCeuticals C E Ferulic: pH 2.0-3.5
- SkinCeuticals Phloretin CF: pH 2.0-3.5
- Paula's Choice Resist C15 Super Booster: pH 3.0
- iS Clinical Super Serum Advance+: pH 3.0-3.5
While I recommend waiting as long as you can in between acids and retinol, that's usually not necessary with acids and vitamin C:
If Your Acid and Vitamin C are Close in pH
When you have two products with similar pH levels (say, within 1.0 of each other), I think you can go ahead and use them at the same time without waiting. This is because they've been formulated to maintain their efficacy at the same level of acidity. So, you could apply your second layer as soon as the first one has absorbed and your skin is dry to touch.
If Your Vitamin C is Not pH-Dependent
If Your Acid and Vitamin C are Not Close in pH
If there's a bigger gap between the pH levels—let's say, a difference of more than 1.0 or 2.0—I'd probably incorporate a bit of waiting time (about 30 minutes) to allow each product to work at its optimal pH range.
However, it might be okay not to wait. Future Derm suggests that applying higher-pH vitamin C derivatives (such as The Ordinary Ascorbyl Glucoside Solution 12%) on acidic skin actually enhances their conversion to L-ascorbic acid. I just haven't been able to find any studies to confirm that. If you come across anything, please let me know!
Again, if you can't be bothered worrying about the whole pH business, feel free to simplify your life and use these ingredients at different times of day!
Now you know the secret to incorporating both acids and vitamin C in your routine.
If you're tight on time, I think the simplest solution is to choose two products that are close in pH, or a vitamin C that is not pH-dependent at all. That way, you can apply them right on top of each other with complete peace of mind. The fact that the acid will make the vitamin C work even harder is a bonus!
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Have you tried AHAs, BHAs or vitamin C?
What results have you noticed?