Skincare Acids: Pretty Much Everything Your Brain Can Handle About AHA, BHA, & Vitamin C

Skincare Acids: Pretty Much Everything Your Brain Can Handle About AHA, BHA, & Vitamin C

Cat Cactus
Cat C.

Jan 24, 2018

Now that you’ve got your hydration down and your skin barrier healthy, you’re ready for that next level of glow: skincare acids. But before you jump on that acid bandwagon, here’s everything you need to know, from AHA to THDA.

It’s a new year, and you’ve got goals — skincare goals, to be precise, a mission to get smooth, blemish-free, glowing skin. You’re armed to the teeth with new knowledge, ready to go all mad scientist in your bathroom and get better beauty through chemistry. You’re ready for acids.

Let’s say that you’ve read the basics on the differences between manual and chemical exfoliation, and armed with Coco Park’s excellent beginner breakdown, you’re ready to add an acid exfoliant to your routine. Congratulations are in order — it took me over a year of hardcore beauty nerdism before I worked up the courage (or desperation) to give acids a try.

Maybe you’ve even tried one in the past, but it didn’t work for you. Maybe you were thwarted by overwhelming irritation on application, or your skin purged too fast (or too slow), or maybe it just didn’t give you a noticeable effect. Don’t despair; finding the right acid exfoliant can be a bit of a matchmaking process until you find the one that’s right for your skin. Not all acids are alike, and you don’t have to shack up with the first one you meet. (Besides, it might smell like unwashed gym socks. That’s right, I’m looking at you, lactic acid!)

With so many options, which acid should you choose? That’s going to depend on what skin concerns you want them to tackle for you, so we’re going break down the big 3: AHA, BHA, and Vitamin C.

Know your goals and the acids to get you there

As tempting as it might be to emulate an established skincare enthusiast’s arsenal of acids, the wrong acids (and routine) for your skin can have disastrous results. (Director of marketing Jude Chao and I put this to the test; disaster confirmed.) There’s an overwhelming amount of information out there, so the simplest way to start is with your goals: What do you want to work on?

Skin Concern



Vit C

Acne (active blemishes)XXHyperpigmentation (from sun, age, acne scars)XXBlackheads (clogged pores)XFirmness (sagging, thinned, loss of elasticity)XXWrinkles (fine lines)XXDullness (loss of luminosity)XXUneven Texture (bumps, closed comedones, large pores)XXRough Texture (dry patches, flakes)XX

Before you head for a new browser tab to fire up your shopping list, there are some concerns you need to consider. Acid exfoliants can be wonderful additions to your beauty routine, or they can leave you worse off than when you started if you don’t use them correctly.

AHA, BHA, L-AA: Alphabet SOS!

The array of acronyms can be overwhelming, but thankfully there’s really only a few that you need to know to get started. If you are unbothered by the alphabet soup of acronyms out there, skip ahead to the breakdown of what sort of skin ghouls they’ll exorcise from your dermises.



HAs are Hydroxy Acids (not to be confused with hyaluronic acid; see below), and there are a few types you’ll encounter. The most common ones are AHAs (Alpha Hydroxy Acids), and BHAs (Beta Hydroxy Acids), and both are widely available with decades of research behind them. A newcomer to the HA squad is PHA (Polyhydroxy Acid), which has successfully been used in clinical trials in place of AHA as an additional ingredient in combination with other actives. Although there’s not much scientific literature yet on the effectiveness of PHA when applied solo, it may be a great alternative for those looking for the perks of AHA without the irritation.

We’ll get into the details of what BHAs and AHAs can do for your skin later, but first we’re going to hit some of the other common skincare acid acronyms you may have encountered.

Vitamin C, aka L-AA, SAP, MAP, THDA

Vitamin C types include L-AA (L-Ascorbic Acid), SAP (Sodium Ascorbyl Phosphate), MAP (Magnesium Ascorbyl Phosphate), and THDA (Tetrahexyldecyl Ascorbate). While vitamin C is not a chemical exfoliant like HAs are, the most effective and affordable form (L-AA) needs a low pH to be stable, which can be irritating for some users. It can also contribute to over-exfoliation when used in a skincare routine that features exfoliants. While Vitamin C serums can be pricey, they don’t have to be; Sheryll Donerson of the K-Beauty Squad is a longtime fan of the OST C20 L-AA serum, which is under $20, or you can even whip one up yourself!


AzA is Azelaic Acid, a powerful anti-acne, anti-aging, anti-redness, anti-inflammatory compound that is so strong that it’s prescription-only in many countries, including the U.S. It’s not for the faint of heart (or moisture barrier) and is best administered by a medical professional.


HA, as in Hyaluronic Acid (not Hydroxy Acid), isn’t an exfoliant at all. It’s a delicious, hydrating humectant found in skincare products of all kinds, often as “sodium hyaluronate” in the ingredients list.

AHA: The skin resurfacer

As you saw in the quick chart above, alpha hydroxy acid can pack a serious skincare punch. AHAs work on the surface of your skin, loosening and dissolving the upper layers of your skin. Have you ever used a paint stripper to dissolve stubborn, flaky paint off a piece of furniture instead of scraping or sanding and risking damaging the wood beneath? It’s the same general concept; manual exfoliation that removes dead skin by scrubbing and abrading the skin can easily damage the layers of fragile new skin underneath, whereas chemical exfoliation dissolves the surface layer so you can gently wipe it away.

That means AHA works for issues on the surface of your skin, such as active acne, rough texture and bumps due to closed comedones, hyperpigmentation (pigmentation due to sun or environmental damage, or acne inflammation), fine lines, loss of firmness, and skin flakes. Blogger Tracy of Fanserviced-b uses AHA as a spot treatment on particularly nasty blemishes, allowing the blemish to surface and then safely drain (with the help of handy COSRX pimple patches) without damaging your skin from picking and prodding. AHA also appears to help thicken skin and stimulate collagen production, making it one of the few ingredients out there that battles aging beyond a superficial plumping of the skin through hydration. (I’m looking at you, skincare commercials. Judgingly.)

With all those anti-acne and anti-aging boxes checked, you’d think AHA would be a shoo-in for any beauty fan’s skincare shelf, but not so fast; not only can AHA can be highly irritating, it’s photosensitizing. That means it makes you even more susceptible to sun damage than if you didn’t use it at all, netting you more hyperpigmentation, rough texture, wrinkles, and loss of elasticity. Do not want.

That makes a daily, high protection, full-spectrum sunscreen an absolute must. Think sun exposure danger is overhyped? Check out this photo of what repeat sun exposure to just one side of your face can do:

Source: The New England Journal of Medicine

Sun damage is no joke! By the way, that SPF label on your moisturizer and makeup? Not going to cut it. Unless you plan on using foundation so thick the Kardashians will be pulling you aside for a “less is more” makeup intervention, you’re not getting the coverage you need. If you can’t commit to daily sunscreen, AHA is not for you.

If you’ve got a skincare closet primed with sunscreen for days and are ready to give AHA a shot, you have a few options for types of AHA:

Glycolic acid is the most common type and is one of the most studied and safest options for people of all skin tones. It’s certainly not the only AHA game in town but is often used to treat deeper skin tones with higher risk of hyperpigmentation, so if your skin is prone to hyperpigmentation, proceed cautiously and research your AHA options. Other popular AHAs include lactic acid, mandelic acid, and as of late, PHA (polyhydroxy acid), all of which may feel gentler and less irritating on the skin than glycolic acid.

AHA is also a humectant, which means even if it’s not at a high enough concentration (5%-10%) and a low enough pH (pH 4.5 or below) for chemical exfoliation to occur, it may still help boost your skin’s hydration and effectiveness of your skincare, giving you smoother, softer skin. If you want those anti-acne and anti-aging better-beauty-through-chemistry perks though, stick to products within those ranges.

BHA: The blackhead battler

While it might seem like beta hydroxy acid is lagging behind AHA in terms of benefits, if I had to choose between BHA and AHA in my routine, BHA wins hands-down. You’ve heard the saying “an ounce of prevention is worth a pound of cure”? It’s easy to say the best way to dodge acne scarring is by preventing the acne in the first place, but it’s harder to put into practice. That’s where BHA comes in. Into your pores, that is, and exorcises the skin demons lurking there.

Unless you’re dealing with hormonal acne (something you should seek medical treatment for), blemishes start from the same root: a blocked pore. BHA is oil-soluble, meaning the oily contents of your pores are no barrier to getting down in there and dissolving the debris lurking there. It’s also a keratolytic, which means it also softens and loosens the upper layers of skin, helping to smooth out skin texture.

This Elizavecca packaging illustrates the evil blackheads in our pores perfectly.

Not only is it perfectly at home spelunking in your pores and thwarting the acne invasion before it starts, it’s also antibacterial and anti-inflammatory. One of the most common BHAs, salicylic acid, is related to the active ingredient in aspirin, in fact! (But not identical, so you can banish those DIY aspirin mask packs to your blacklist of skincare sins.)

It doesn’t need to get any better, but it does: unlike AHA, BHA is not photosensitizing and in fact can help boost the effectiveness of (but not replace!) your sunscreen by partially filtering some UV. As someone with oily, clog-prone skin, BHA is forever my bro in the lifelong fight to keep blackheads at bay.

To get the pore-clearing benefits of BHA, look for a concentration of 1%-2% for salicylic acid, or the equivalent strength in an alternate BHA, like the gentler betaine salicylate, and a pH below 4 for exfoliation. You may still get benefits outside those ranges, such as soothing inflammation.

Vitamin C: The glow getter

Looking at the initial chart, you might conclude that vitamin C (aka ascorbic acid) is superfluous; AHA can do everything that vitamin C can do, right? Not quite. While it’s true that AHA is hogging most of the checkmarks, it also has some major downsides that make some people run for the hills. Vitamin C is right at the forefront in the fight against aging, slinging antioxidant reinforcements to struggling skin cells and boosting collagen production to turn the tide against fine lines.

Not everyone needs an anti-acne arsenal on their skincare shelf; so if your goals include fading hyperpigmentation (including sun and age spots), smoothing skin texture, firming skin, repairing fine lines, and restoring the luminosity of your skin, vitamin C is here to make the magic happen.


Vitamin C is also photoprotective; while it can’t replace sunscreen (sorry, fellow sunscreen slackers, nothing can), it works in tandem with your sunscreen by repairing UV damage deep below the skin. Since sun exposure is the primary cause of visible aging, vitamin C is a key tool in an anti-aging arsenal, whether you're more focused on preventing future signs of aging or want to repair some existing damage.

It’s good for acne sufferers too; increased collagen production means better healing, and it tackles post-inflammatory hyperpigmentation (aka PIH) left behind by acne. When you’re battling blemishes, a healthy moisture barrier is a resilient moisture barrier, helping you bounce back faster from breakouts.

Vitamin C is an excellent overall brightener as well; even if you don’t have defined hyperpigmentation, vitamin C can seriously up the overall luminosity of your skin. It can also be used daily to replenish your skin’s supply of free radical-fighting antioxidants; the effects last about 24 hours so there’s no need to apply it more than once a day.


The most potent and widely-studied form of Vitamin C is L-Ascorbic Acid, aka the type that’s producing all those sexy results in clinical trials. The problem with L-AA is that it’s volatile; it oxidizes rapidly when exposed to light, heat, and air, losing its spunky antioxidant army in a war of attrition instead of in combat with the free radicals ravaging your skin.

L-AA is stable at a pH of 3.5 and lower, which makes it irritating for some people. Concentrations should be between 10%-20%; at above 20% the absorption rate goes down, so there’s no need to go higher than 20%. Look for an L-AA with a concentration of 10%-20%, pH of 3-3.5, and in an airless pump or dark bottle. Remember light, heat, and air will render your L-AA useless, so clear glass bottles and warm environments (like your bathroom) are a no-go.

There are other forms of vitamin C, but their performance in clinical trials has been lackluster compared to L-AA, or there’s been limited research done. If L-AA is too irritating for you, check out products containing the more stable options MAP, SAP, or THDA (see definitions above), but just be aware that results may be more limited or take longer to appear.

Ready to give them a try?

Generally, acids do best on bare, freshly cleansed skin. There’s a lot of different ideas about whether wait times are needed with acids, which we’ll talk about in a separate post. Regardless of whether you use wait times between acid exfoliants and other products, think of applying acid exfoliants as a final cleansing step. Then move on to the rest of your routine!

If you’re not using products with the concentration and pH needed to act as an exfoliant, don’t worry about the product order and just use them as directed on the label. Remember, acids can have additional benefits outside the concentration and pH required for exfoliation, but if you want serious results, you’ll need to find a serious acid to deliver them.

Need a starter list? Here’s a few top picks from the K-Beauty Squad:


Mizon 8% Peeling Serum

COSRX AHA 7 Whitehead Power Liquid

Swanicoco AHA 10% Coco Soft Peeling Cream (now rebranded as the A-PHA Purifying Peeling Cream)

Paula’s Choice Resist Weekly Resurfacing Treatment with 10% AHA

Biologique Recherche P50


COSRX Blackhead Power Liquid

Purito Centella Green Level All In One Pad

Paula’s Choice Resist Daily Pore-Refining Treatment With 2% BHA

Paula’s Choice Resist BHA 9 Treatment

Vitamin C:

OST C20 (now rebranded as Tia'm My Signature C Source Serum)

SkinCeuticals C E Ferulic

Holy Snails El Dorado Vitamin C Oil Serum

Have any questions, or recommendations on skincare acids that are in the sweet spot of concentration and pH? Let us know in the comments, or share this article on your Beauty Wall and see what your friends think!

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