I remember when exfoliating acids first emerged on the scene in the early ‘90s. The first time I ever got my hands on a professional-grade glycolic acid peel in 1992, I ended up burning the skin on my face (oops). I was new to acids—as was the rest of the professional skincare world—and I didn’t really know what I was doing yet. Acids have come a long way since then with their stability and are now the go-to in many skincare routines.
As popular as acids are, there’s a lot to know and they can still be pretty confusing. To clear a few things up, I compiled a list of the questions I get asked most when it comes to acids. I hope you find the answers you’re looking for!
Meet the Acids
Before diving into FAQs, I thought I’d go back to basics and give a brief description of each type of acid, what it’s derived from, and what it’s best for.
Alpha Hydroxy Acids (AHAs)
Alpha Hydroxy Acids, also known as AHAs, are a group of organic acids derived from natural foods. One shared characteristic of all AHAs is that they are water-soluble. AHAs are used in skincare more than any other group of acids thanks to their ability to treat a variety of skin concerns. This includes dry or dull skin, fine lines, wrinkles, uneven skin texture, post-breakout scars, and hyperpigmentation (sun spots and melasma).
- Lactic Acid: This AHA is naturally derived from milk, but a synthetic version is usually used in cosmetics. Lactic acid gently dissolves dead skin-cell buildup on the surface of the skin. It’s also a natural moisturizing factor (NMF), making it good for hydration and barrier-repair. If you have dry or sensitive skin and want a brighter, healthier complexion, lactic acid is a great choice.
- Glycolic Acid: Glycolic acid is naturally derived from sugar cane and has a smaller molecule size than any other AHA. This means it can penetrate deeper into the skin, making it more potent but also potentially more irritating. Glycolic acid is especially effective at targeting issues like hyperpigmentation, fine lines, and wrinkles. Glycolic acid is also particularly good at stimulating collagen growth over time.
- Mandelic Acid: Mandelic acid is naturally derived from bitter almonds and is very gentle. For true exfoliation, it works best when combined with other exfoliating acids. It can play a supporting role in suppressing pigmentation and some studies have shown it may help with acne.
- Malic Acid: Malic acid is naturally derived from apples and works well as a humectant. It also works well as a pH adjuster in products. This acid is best for aging, pigmentation, and dryness.
- Tartaric Acid: Tartaric acid is naturally derived from fermented grapes, which means it also has antioxidant properties. It’s a gentle, mild exfoliator that can also be used as a pH adjuster.
Beta-Hydroxy Acids (BHAs)
The key difference between AHAs and BHAs is that BHAs are oil-soluble. This means that, instead of working exclusively in the upper layers of the skin, BHAs can actually cut through the skin’s natural oils and penetrate into the pore lining to dissolve blockages. If acne, clogged pores, and oily skin top your list of skin concerns, BHAs are hands-down the best option for you.
- Salicylic Acid: Salicylic acid is the only BHA available in skincare and is naturally derived from willow bark. It’s a great ingredient for dissolving keratin plugs inside pores and reducing clogged pores. Salicylic acid also has antibacterial and anti-inflammatory properties. One thing to be aware of is that salicylic acid can cause dryness in some people, so you’ll want to look for a formula that includes hydrating ingredients.
Poly-Hydroxy Acids (PHAs)
Poly-Hydroxy Acids (PHAs) are a lesser-known group of exfoliating acids that were patented by NeoStrata around 1994 (though they were first discovered in the early ’70s).
PHAs target many of the same issues as AHAs, but they have larger molecules than both AHAs and BHAs. This means they are incredibly gentle and unlikely to cause irritation. Their claim to fame, however, is that this doesn’t make them any less effective as exfoliators. Much like AHAs, PHAs also function as humectants to hydrate the skin.
The two PHAs typically used in skincare formulations are gluconolactone and lactobionic acid. Because they’re structurally similar AHAs, PHAs are sometimes positioned as a milder alternative that offers similar results. PHAs also offer antioxidant benefits.
If you have very sensitive skin or even rosacea, PHAs may be an ingredient for you to consider. We don’t currently include them in any of our products, largely due to the licensing costs associated with them.
Our last acid, azelaic acid, is kind of in a class of its own. It’s chemically a dicarboxylic acid and while it exfoliates the skin a little, this isn’t its main claim to fame. Azelaic acid can be found in wheat and rye and, in small amounts, is naturally present in the yeast on our skin.
Azelaic acid has antibacterial properties that make it effective in the treatment of acne. It’s great for those with crossover conditions because it’s a very soothing ingredient that has the ability to calm redness and irritation. In fact, it’s often used in prescriptions for rosacea. If you’re someone who deals with both acne and rosacea and can’t tolerate traditional acne treatments, azelaic acid could be a beneficial ingredient for you to consider.
Azelaic acid is also very effective at treating hyperpigmentation, whether it’s melasma, sun damage, or post-breakout marks. In fact, some studies have shown that, in certain concentrations, azelaic is more effective than hydroquinone when it comes to fading hyperpigmentation and brightening the skin.
Azelaic acid is safe to use if you’re pregnant or nursing, so it can be a good alternative to other ingredients.
Exfoliating Acids FAQ
These questions topped the list of most-asked questions when it comes to exfoliating acids.
How Do Exfoliating Acids Work?
Exfoliating acids work by lowering the pH level of our skin. To be effective, an exfoliating acid must have a pH below 4 (our skin’s natural pH hovers right around 5). When applied topically, acids put the skin into an acidic state. This allows the bonds (or “glue”) that hold dead skin cells together to be dissolved, at which point expired cells can be shed from the skin to reveal the fresh, healthy cells underneath.
Our skin has a natural exfoliation process called desquamation. All this means is that new skin cells are born in the deepest layers of our skin, slowly working their way to the surface until they push out old, expired cells. This process slows down as we age (or is naturally slow for some people to begin with, which can contribute to breakouts). Exfoliating acids helps us shed dead skin cells more efficiently, encouraging the skin to act in a younger, healthier way.
What Benefits Do Acids Give?
Exfoliating acids can benefit the skin in so many ways because they ultimately encourage the skin to act in a younger, healthier way by shedding dead skin cells more efficiently. Benefits include the following:
- Improve hydration by removing surface dryness (many AHAs also act as humectants)
- Fade pigmentation from post-breakout marks or sun damage
- Reduce the appearance of large pores, fine lines, and wrinkles
- Encourage a brighter-looking complexion by removing dull, dead skin cells
- Improve overall skin texture
- Reduce redness and acne breakouts
- Prevent clogged pores by shedding dead skin cells so they don’t fall into pores and block them
- Increase the efficacy of other skincare products by removing the barrier of dead skin cells
Which Acids Are Safe for Pregnancy?
ALL except salicylic acid. Be sure to talk with your doctor though because some have different viewpoints about this.
Which Acids Are Best for Mature Skin? For Younger Skin?
Everyone’s skin is different, so there isn’t one blanket answer, but my best advice would be to observe the pH level of an acid product as well as the percentage of acid included.
When you’re younger, your skin has less of a need for acids since your cell turnover is already functioning well, unless you have clogged pores or acne. Young skin also tends to be oilier, so I recommend BHA (salicylic acid) since it’s oil soluble and can really get into the pores to clean them out. However, younger skin, even though it’s thicker, is more reactive to active ingredients so go easy. You can still use AHAs, just look for a formula that is gentle with a lower percentage of acids.
Mature skins should focus more on AHAs to aid in the shedding of dead skin cells and the building of collagen. Even though the dermis is thinner in older skin, the epidermis is thicker and is harder to penetrate so the skin can tolerate a higher percentage of acids.
To give you an idea of percentages, I usually recommend my Pro Results Power Serum to my mature clients who are dealing with sun damage and wrinkles, and this includes a 20 percent AHA blend. For clients in their late twenties or early thirties, I like to recommend Pore + Wrinkle Perfecting Serum, which is a 17% AHA blend (and includes salicylic).
What is the Best Way for People With Sensitive Skin to Use Acids?
Sensitive skin can benefit from exfoliation as much as any other skin type, but there are a few guidelines to keep in mind so you don’t end up harming your skin (this also goes for those of you using prescription retinoids).
First and foremost, you should never be exfoliating every day (even if you don’t have sensitive skin). No one builds up dead skin cells quickly enough to exfoliate this often, and you’ll just end up damaging your skin’s protective barrier (aka making sensitivity worse). Limit your use of exfoliating acids to three to four times a week. (Five at the most.)
Second, make sure you’re using the right acid formula for your skin type. Lactic acid is a great choice for sensitive skin and can even work well for those with rosacea. It has soothing, hydrating properties and, when used correctly, can help repair barrier damage, which is often the underlying cause of sensitivity. You can still use a formula that includes multiple acids, just keep an eye out for one that’s heavier on lactic.
Finally, keep the pH and percentage in mind. The lower the pH of a product and the higher the percentage of acids included, the more potent the formula. These are two factors you can play around with until you find the sweet spot for your skin.
Should I Use Acids in a Toner or Serum?
I advocate exfoliating acid serums over toners for two reasons: an exfoliating serum is less likely to cause irritation, and it works deeper and more effectively than an acid toner.
Exfoliating acid toners are more likely to irritate the skin because they provide a quick hit of acids to the skin all at once. They are fast-acting, and while a lot of people like the quick results they give, they can also quickly damage your barrier. Acid toners are usually water-based, so they evaporate quickly and don’t provide long-lasting benefits. This water evaporation also runs the risk of leaving your skin feeling tight and dehydrated.
Exfoliating acid serums, on the other hand, tend to have a thicker consistency that can coat the skin and allow for a slow, steady release of acids. This means less irritation, longer-lasting results, and an added benefit of hydration to keep skin acting healthy.
Learn more about the pros and cons of acids in a serum vs. toner.
At What Age Should Someone Start Using Acids?
If you have acne and clogged pores, you can start using salicylic acid as early as fifteen. This will be beneficial for clearing and preventing clogged pores as well as fading acne marks. If you don’t deal with acne and are just using acids for a smoother texture and all-around healthy glow, the youngest I would start is probably twenty.
How Can You Tell if You’re Using Acids Too Often?
As I mentioned, daily exfoliation is too much regardless of your skin type. While using acids properly can help strengthen your skin’s barrier, overusing them can damage it. The line between the two can be a fine one, but here are some signs you may be exfoliating too often:
- Stinging. It’s normal for acid products to tingle when applied to the skin, but this should subside as you start to use them regularly and your barrier becomes healthier. If you’re applying exfoliating acids and keep getting a stinging sensation, you may want to dial it back.
- Dryness. Again, properly using acids should improve your moisture barrier and improve your skin’s ability to hold on to hydration.
- Redness. This could be a sign that you’re overdoing it and actually giving your skin micro burns. If your skin keeps getting redder in its appearance, this might be a sign of overuse.
When in doubt, dial it back.
Do Dry Patches Mean You Should Exfoliate More or Less?
This is a tough one. Acids can be used to correct dryness, but dryness can also be one of the signs you’re overusing them.
If you’re getting dry patches in addition to redness or stinging, try cutting back on acids first.
Physical Exfoliants in Addition to Acids
On the other hand, you might just need to add in another type of exfoliation. I would say don’t rely solely on acid exfoliators to get rid of dry patches. Some people shy away from them or view them as “old school”, but I believe everyone can benefit from a gentle, physical scrub. The benefit of physical exfoliation is that it can physically lift off dry patches as well as pigment cells (discoloration) once they’ve been loosened up by acids.
If you have stubborn dry patches, try a gentle scrub with non-plastic, rounded beads or you can even use a soft baby washcloth when washing your face. This can be a great supplement to acids (but for most skin types, you don’t use both methods of exfoliation on the same day).
FYI, there are three types of exfoliants: acids, enzymes, and physical scrubs. Learn which exfoliant should you use and how often.
Can You Use More Than One Type of Acid?
Yes, in fact, I encourage it! All of my exfoliating acid serums are formulated with more than one type of acid to give maximum benefits. For example, salicylic acid can clear the way for AHAs like glycolic and lactic by cutting through oil and penetrating the pore lining. Combining glycolic acid with other AHAs can be beneficial since it has a smaller molecule size. Adding lactic acid to an exfoliating acid product can make it more hydrating.
The key is to look for a product that’s heavier on the type of acid that caters to your specific skin concerns.
Should Acids be Used in the AM or PM?
My philosophy is that acids are better for nighttime use. Think about what your skin is doing during the day versus at night. Daytime is all about protection and preventing environmental damage. Acids can put your skin in a slightly more vulnerable state by exposing fresh baby cells, which is not at all what you want in the morning.
Nighttime is all about repair, and I definitely think of acids as reparative (not protective) ingredients.
Want to know more about how your skin differs from day versus night? Learn about how circadian rhythms affect the skin and what this means for your skincare routine.
How Should You Layer Acids With Other Ingredients?
After cleansing your face and applying an alcohol-free toner, your acid product should be the first thing touching your skin so it can effectively lower the pH of your skin. Wait about one minute before applying your next product. A good exfoliating acid serum should provide hydrating benefits as well as exfoliation, but if you’re using a hydrating serum, apply that next. Moisturizer will be your last step.
Can You Use Exfoliating Acids if You Use Retinol or Retinoids?
Yes, in fact, you should absolutely use both to get the best results (just not at the same time). Retinol and prescription retinoids work on the skin from the inside out, increasing the rate at which new skin cells come to the surface (remember desquamation?). This means that the rate at which expired cells build up on the surface of the skin also increases, so it’s essential to make sure they’re sloughed off using an exfoliating acid serum and a gentle, skin-polishing scrub.
Which type of acid serum you use will depend on your skin type. Read more about how to successfully use both retinol and acids in your routine.
Can Acids be Used with Vitamin C?
Yes, but with a few caveats. As I already mentioned, I believe exfoliating acids should be used at night to help the skin repair itself. Vitamin C is great at defending the skin against environmental damage, so it should be used in the morning. Just be careful about what kind of vitamin C you use. Like exfoliating acids, it’s an acidic ingredient, and putting the skin in too much of an acidic state can cause serious damage and irritation. L-ascorbic acid is usually the biggest culprit when it comes to irritating people’s skin because it’s very acidic and unstable. (Hence why it can sting on contact.)
Can Acids be Used in the Summer?
Yes, as long as you’re diligent about sunscreen use. The whole point of acids is to improve and repair the skin, and summer sun is obviously a huge source of skin damage. Acids are a useful tool for combatting this damage, but only if you use sunscreen to protect your skin in the first place. You won’t get the best results from acids or any other reparative ingredients if you don’t do your best to prevent sun damage in the first place.
Will Acids Help With PIE or PIH?
Post-inflammatory erythema (PIE) is the term for red marks left behind by blemishes or other injuries to the skin. Post-inflammatory hyperpigmentation (PIH) refers to the dark, pigmented marks that sometimes form after PIE and tend to linger for a long time.
Exfoliating acids can help with both, but more so PIH. All acids will help, but glycolic acid is especially effective at fading pigmentation. Learn what else you can do to fade post-breakouts marks.
Can Acids Help With Blackheads and Sebaceous Filaments?
Yes, specifically salicylic acid since it’s oil soluble and can penetrate the pore lining. Both blackheads and sebaceous filaments must be manually extracted to be truly removed, but using a salicylic acid serum a few times a week will keep pores clear. This can help prevent both blackheads and sebaceous filaments and minimize their appearance.
Here’s my three-step plan for reducing blackheads.
Can Acids be Used on the Neck? What About the Body?
Acids can be used on the neck, but I recommend patch testing first because this skin can be quite sensitive. It may not be able to tolerate the same strength of acids as the skin on the face, and you may not want to exfoliate this area as often.
Acids are great for the body and work very well for keratosis pilaris.
What Are Best Practices for Using Acids Around the Eyes?
First and foremost, don’t get too close to the under-eye area. Your lashes can pick up and transfer products containing acids to the eyes, which can cause stinging. Bring a product up to but not past the orbital bone.
Look for a product specifically formulated for the eye area—it will be more gentle and contain a lower percentage of acids. Once you’ve applied an exfoliating product around the eyes, follow up with a moisturizer.
I’m actually a huge fan of using an under-eye exfoliator and I have one in my line. It’s a great way to minimize fine lines and wrinkles and to ensure your eye cream performs better.
Are Acids Vegan?
For the most part, yes. In its natural form, lactic acid is derived from milk, so it wouldn’t be vegan. The majority of lactic acid used in cosmetic products is now synthetically produced, though, so it is vegan. Be sure to look at the other ingredients in the formula since these may not be vegan.
Learn which Renée Rouleau products are vegan.
What Does it Mean When an Acid Tingles?
It’s normal for a product with a lower pH than your skin to cause tingling. This sensation is caused by a product hitting your nerve endings, which are exposed when you have cracks in your moisture barrier. When the tingling stops, this is a good sign because it means your protective barrier is intact and all sealed up. The goal is ultimately to get to no tingling, and no—this doesn’t mean a product has stopped working. Just that your skin is healthier!
Can Your Skin Get “Used” to Acids? Should You Switch Up Acids for Better Results?
In general, your skin can get used to acids in the sense that it gets to a healthier state so acids aren’t as much of a shock to it. This does not mean, however, that acids are becoming less effective. Using a product long-term does not make your skin “immune” to it.
The only reason you would need to switch up the type of acid product you’re using is if your skin’s needs have changed. If you’ve been using an acid product for a while and aren’t getting the desired results, you may just need a formula with different percentages. However, keep in mind that you have to have realistic expectations of any skincare product, as well as patience to give it time to work!
In summary, I’m a huge believer in acids. I think that using them for the past thirty years has greatly contributed to the look and condition of my skin today at age fifty. I love all the wonderful benefits exfoliating acids can provide, and I hope this post makes it easier for you to figure out what works for you!
Celebrity Esthetician & Skincare Expert
As an esthetician trained in cosmetic chemistry, Renée Rouleau has spent 30 years researching skin, educating her audience, and building an award-winning line of products. Trusted by celebrities, editors, bloggers, and skincare obsessives around the globe, her vast real-world knowledge and constant research are why Marie Claire calls her “the most passionate skin practitioner we know.”