Written by: Shannon Steck
Medically Reviewed by: Corey L. Hartman MD Board-Certified Dermatologist
In this article:
What are alpha hydroxy acids?
Benefits of AHA for skin
How do alpha hydroxy acids exfoliate the skin
Does AHA help with dark spots?
How long will it take to see results from using AHA?
What are the six most common alpha hydroxy acids?
How to use an AHA exfoliant
Can you use AHA every day?
Who should use an AHA exfoliant?
AHA exfoliant tips from our experts
What can you not mix with AHA?
Is AHA the same as retinol?
Side effects of AHA
If you’re on a quest for younger-looking, smoother and more even-toned skin, you may have heard of alpha hydroxy acid (AHA). This group of multi-tasking ingredients is commonly recommended for tackling a plethora of skin concerns and for good reason: Extensive research has made it clear that AHAs are essential for smooth, even-toned, hydrated skin (1). Did we also mention a leave-on AHA product is among the best ways to exfoliate?
But what are AHAs and how exactly do they work? Given there’s more than one AHA, which alpha hydroxy acid should you use to achieve your skin goals?
Let us answer all these questions for you below in our expert-approved guide on all things AHA.
What are alpha hydroxy acids?
AHA stands for alpha hydroxy acid— but don’t let the word “acid” scare you: AHA ingredients are safe on all skin tones and are gentler on your skin than most scrubs or cleansing brushes could ever be.
Alpha hydroxy acids are a group of natural and synthetic ingredients that, when properly formulated, exfoliate the uppermost layers of skin (2). Board-certified dermatologist Dr. Corey L. Hartman says, “They reduce the bonds between skin cells that allow them to dissociate more freely, but in a controlled manner.”
Doing so reveals fresher, refined skin that appears much smoother, is more hydrated, and, over time, becomes visibly firmer. Anyone concerned with looking younger, longer should consider adding an alpha hydroxy product to their skin care routine.
There are several skin exfoliating AHAs, but the two most effective, common, and well-researched are glycolic acid and lactic acid. Other AHAs— malic acid, citric acid and tartaric acid— also have benefits, but research on them is limited in comparison.
Benefits of AHA for skin
Alpha hydroxy acids are multi-tasking skin care ingredients that offer numerous benefits for skin, including:
- Exfoliation: AHAs slough off dead, dull skin from skin’s uppermost layers, allowing skin’s natural, healthy glow to shine through.
- Hydration: Beyond exfoliating, AHAs function as humectants, meaning they work to bind and attract water to skin, leaving it hydrated and balanced (3).
- Anti-aging: This group of ingredients works to plump skin through added hydration, reduce the look of fine lines and wrinkles, boost firmness and elasticity and promote a youthful appearance overall (4).
- Discoloration fading: AHAs help visibly fade dark spots, allowing a more even skin tone (5).
- Sun damage: AHAs work to help nourish sun-damaged skin through hydration, skin firming and combating signs of visible sun damage (6).
- Breakouts: AHAs rid skin of dead cells that would otherwise go on to possibly cause breakout-related clogs. Most research demonstrating AHAs’ breakout busting abilities detail higher concentrations of these ingredients usually seen in professional chemical peels (7).
- Boost effectiveness of other skin care products: AHAs enhance absorption of skin care products through ridding the skin of the dead, dull top layers that would otherwise prevent or slow absorption of beneficial ingredients.
How do alpha hydroxy acids exfoliate the skin
When we’re young, our skin naturally sheds built-up layers of dead cells at a rapid rate. But, as the years pass, several factors slow this process, bringing it almost to a halt. Culprits like unprotected sun exposure, dry skin, oily skin and other skin problems can make skin dull, dehydrated and older-looking. The glow goes and dullness grows.
A leave-on AHA exfoliant or exfoliating toner works on the uppermost layers of skin, loosening the bonds between dead surface layers and the radiant skin beneath. An occasional-use rinse-off AHA exfoliant peel tends to be more potent, offering multi-level exfoliation with a higher concentration of acids that do their jobs faster, often within minutes.
And, while AHAs have benefits for all skin types—diminishing the look of lines and wrinkles, improving skin’s firmness, texture, and tone—their standout hydrating properties and ability to improve visible signs of sun damage make them ideal for normal to dry skin with advanced signs of aging (9).
It’s important to note that formulary concerns are crucial for a product to be both gentle and effective. Research has shown that AHA exfoliants containing glycolic acid or lactic acid in concentrations between 5% and 10% and with a pH between 3 and 4 are ideal for optimal, youth-reviving, non-irritating exfoliation. Higher concentrations are best used occasionally and in the form of rinse-off exfoliants.
Does AHA help with dark spots?
As touched on above, alpha hydroxy acids can help reduce the look of dark spots related to sun damage, aging, breakouts and sensitivity (8).
Most studies which detail AHAs’ ability to drastically tackle dark spot concerns study their effects when used in higher percentages (20%+) and when combined with other ingredients, like beta hydroxy acid and vitamin C, and in-office procedures, like various types of light-emitting and laser therapies.
Overall, tackling dark spots requires a multi-ingredient approach. Using a higher-percentage leave-on AHA exfoliant alongside application of a vitamin C serum and tranexamic acid treatment product can help tackle dark spots (even the stubborn ones) efficiently.
However, no matter how many effective ingredients you use in conjunction with AHA, little progress will be made on dark spots if you don’t apply (and reapply) sunscreen. AHAs increase skin’s sun-sensitivity, meaning that if not used with a broad-spectrum SPF 30+, these ingredients can actually worsen the look of dark spots (But you’re using SPF already anyway, so there’s nothing to worry about, right?).
How long will it take to see results from using AHA?
Alpha hydroxy acids begin to work almost immediately when formulated in leave-on formats (toners, liquid exfoliants) to reveal brighter, glowy skin. It takes a bit longer, about 2-4 months, to visibly recognize AHA-related anti-aging benefits, like a decrease in appearance of fine lines and wrinkles (4). Other results, such as smoother texture and a more radiant look, will be apparent within days.
Results are heavily reliant on the AHA products you use (pH, ingredient concentration, packaging) as well as how often you use them. Application of a 10% lactic acid exfoliant 3x a week will garner visible benefits quicker than applying a 5% lactic acid serum 1x a week.
The exception to the 2-4 months visible results rule? In-office AHA chemical peels. These high-percentage treatments work much quicker than at-home AHA topical skin care products. Speak to a dermatologist about these treatments for specific result timelines.
What are the six most common alpha hydroxy acids?
There’s a myriad of different AHAs, all with varying origins, molecule sizes and skin benefits. You’ve most likely heard of glycolic acid and lactic acid, the cool kids of the alpha hydroxy acids, but have you heard of mandelic acid? What about malic acid? Let’s dig into the six most common AHAs in skin care.
Glycolic acid
Among all of the alpha hydroxy acids, glycolic acid is the gold standard. That’s because it’s the most researched and, along with lactic acid, has the best track record of impressive results for most ages and all skin types (10).
What makes glycolic acid so special is its small molecule size which enhances its ability to penetrate the uppermost layers of built-up skin to reveal the better-looking skin hiding beneath. It also has a natural ability to hydrate skin, “teaching” it to become better at retaining its natural moisture. Dr. Hartman notes, “it is a natural humectant, drawing water into the skin and providing a hydrated glow as it exfoliates.”
If that weren’t enough, glycolic acid used alone or with other AHAs at concentrations of 5% and up helps enhance skin’s look of firmness and resilience while softening other signs of sun damage.
Although glycolic acid can be derived from sugarcane, the synthetic form is the one most often used in skin care products because it’s easier to stabilize and ensure consistent percentages. We offer several glycolic acid exfoliants if you’re looking for this AHA superstar ingredient in a product.
A common myth is that darker skin tones can't use glycolic acid because of being prone to dark spots; however, this skin care acid is actually effective at reducing the appearance of dark spots on all skin tones and can be gentle for all skin types depending on overall formulation.
Lactic acid
Lactic acid does everything glycolic acid does, but just at a bit slower pace because its molecule is a little bit larger, which slightly reduces its ability to penetrate skin’s outermost layer. Topical lactic acid in concentrations of 2% and up can hydrate skin. When used alone or with other AHAs, it begins working as an exfoliant at a 5% concentration, with amounts between 5% and 10% considered ideal for skin care products meant to exfoliate. Dr. Hartman notes that, “it shines at reducing the appearance of dark spots and providing a more even complexion” (11).
Although lactic acid can be derived from milk, the synthetic form is used most often in skin care products because, just like synthetic glycolic acid, it’s easier to stabilize and ensure consistent results.
Malic acid
Malic acid is larger than glycolic and lactic acids, but is still able to exfoliate, and it also delivers antioxidant benefits (12). Malic acid in concentrations of 1% to 2% is a good supporting player when included in AHA exfoliants led by glycolic and lactic acids—you get a nice multi-level exfoliation. You’ll find such blends in select leave-on exfoliants as well as rinse-off peels.
This AHA can be derived from apples or produced synthetically; the synthetic version is the popular choice for skin care for the same reasons mentioned above for glycolic and lactic acids.
Tartaric acid
Tartaric acid is larger in size than malic acid and is nearly twice as large as glycolic acid. It occurs naturally in grapes (and it follows, in red wine), but is also made synthetically, which is the form typically used in skin care products.
Although tartaric acid can exfoliate skin when used in roughly the same concentrations as glycolic or lactic acids, it functions best in helping to maintain the pH range that other AHAs need to work their magic (6).
In certain formulas, it helps provide more targeted exfoliation, as each size of AHA has its layer-by-layer benefits.
Fun fact: tartaric acid in wine plays a major role in maintaining color, stability, and flavor.
Citric acid
Citric acid comes from various citrus fruits but also can be made synthetically. Although in higher concentrations (around 10% and up) it can exfoliate skin, it’s also considered more irritating due to its naturally lower and skin-sensitizing pH of 2.2.
Low amounts—typically 1% or less—of citric acid show up in many skin care products where it works as an antioxidant as well as a pH adjuster, keeping formulas within the pH range they need to be effective yet gentle (13).
Some AHA products contain citrus extracts that the brand claims work like natural AHAs. That sounds good but published research hasn’t proven such extracts are useful to exfoliate skin and their fragrant components (such as limonene) can be sensitizing.
Mandelic acid
Mandelic acid shouldn’t be overlooked as an AHA option. Its larger size—it’s the biggest AHA—means slower penetration into skin, making it an intriguing choice for gentle exfoliation, especially for sensitive skin. Studies suggest that mandelic acid is a great option for melanated skin (14). It’s also especially good at fading post-acne marks, technically known as post-inflammatory hyperpigmentation.
This AHA slowly exfoliates skin, allowing youthful, more radiant skin to shine. Research has also shown that mandelic acid (when used at 40% strength as a rinse-off peel) can prompt skin to make more oil—not great news for oily or breakout-prone skin, but helpful for those with dry skin (15).
How to use an AHA exfoliant
It often takes some experimenting to see which AHA works best for your skin. Some people can use higher concentrations (such as 10%) without a problem, while others find that lower concentrations (such as 5%)—or alternating the use of higher and lower strengths—is the ideal solution.
Whichever leave-on exfoliant or exfoliating toner you choose, it should be applied after cleansing and toning with a traditional hydrating toner. The other products in your routine, like serums, boosters, and moisturizers, go on after your exfoliant in order from thinnest to thickest texture. Don’t forget to finish with sunscreen during the day.
Can you use AHA every day?
Low-to-mid level (2%-10%) concentration AHA products can be used every day, as AHAs help normalize skin’s healthy appearance. Rinse-off products like cleansers with AHAs can also be used frequently (2x a day).
However, this doesn’t mean you should purchase a 10% AHA exfoliant and begin using it twice a day. If you’re new to AHAs, slowly integrate them into your skin care routine. Start with applying a low concentration AHA product (2%-5%) once a week and note skin’s response. If your skin responds positively, increase application. You can also use face masks with a high percentage of AHAs, like 25%, once a week or bi-weekly.
Once your skin’s acclimated to AHAs, you can begin experimenting with AHA product textures (water-light liquids, lotions, gels), concentrations and ingredient combinations (more on that to come!).
Who should use an AHA exfoliant?
Everyone can use, and benefit from, an AHA exfoliant. They’re best for those with dry skin, sun damage, dullness and aging concerns.
Seeing as there’s quite the library of different AHAs in different concentrations to choose from, there’s pretty much an AHA for every skin type and expertise level:
- Sensitive skin types, or those with an easily compromised barrier, might respond best to low concentrations of mandelic acid due to its large molecule size and small chance of sensitization.
- Frequent AHA users, or those with normal, combination or oily skin, will likely benefit from glycolic and lactic acids.
- Those new to AHAs should begin usage at low concentrations (2%-5%).
- Postpone AHA application if skin is sunburned, irritated, being waxed or lasered or has open cuts or wounds.
AHA exfoliant tips from our experts
Looking to reap all the benefits of the AHA products we’ve outlined above? Follow our expert-approved tips below:
- You don’t need to wait between steps for each product to absorb. The AHA will work even if you apply another product immediately before or after. Doing so won’t throw off the exfoliant’s pH.
- It’s fine to apply an exfoliant to your undereye area, up to the edge of the orbital bone.
- Although daily exfoliation is optimal for many people, you might find that exfoliating every other day works best for you. Again, it takes some experimentation.
- Don’t apply an AHA body lotion to freshly shaved legs. Shaving is a form of exfoliation, so no need to double up on those days.
- Make sure to apply a liberal amount of broad-spectrum SPF 30+ daily to avoid the redness and burning associated with the increased UV sensitivity that AHA causes.
What can you not mix with AHA?
Some seriously confusing misinformation obstructs the hard-hitting truths surrounding AHAs. For example, would you be shocked to learn that you can use AHAs with other skin care ingredients, like retinol and vitamin C? It’s true!
We've busted the myth that you can't use retinol and AHA together extensively over the years, but when used in the same skin care routine or the same peel, retinol and AHAs (specifically glycolic and lactic acids), can enhance each other's benefits and better tackle stubborn skin care concerns related to aging and dark spots (16).
Antioxidants, specifically vitamin C, niacinamide and vitamin E, can also coexist peacefully with AHAs in the same regimen. Studies show that a skin care system which made use of AHAs alongside these antioxidants improved visible signs of aging skin, including texture, tone and firmness “without significant adverse effects” (4).
Although these ingredients can be used together or within the same skin care routine, you should always monitor your skin’s response and adjust accordingly. And of course, ensure all of your skin care products are free from ingredients proven to provoke irritation, such as denatured alcohol and strong fragrance.
Is AHA the same as retinol?
AHAs are not the same as retinol. Because these ingredients both reveal younger looking skin, it’s often thought that they function in similar ways, but this isn’t true.
AHAs are exfoliating ingredients that loosen the bonds between dead skin cells, allowing dull skin to slough off as it did when we were younger.
Contrary to popular belief, retinol does not exfoliate skin! Retinol, and other vitamin A derivatives, are smart ingredients that communicate with skin and encourage cell turnover, which is skin’s process of replacing dead, dull surface-level cells with new ones (17).
Side effects of AHA
Although AHAs are gentler chemical exfoliants, they can cause minor side effects. These effects vary from person to person based on skin type, frequency of application, skin care practices and the AHA percentage applied.
AHA is an active skin care ingredient, meaning those new to AHA may experience some side effects while their skin adjusts to these hard-working ingredients.
According to the United States Food and Drug Administration (FDA) the most common side effects reported are (18):
- Increased instance of sunburn, dark spots and redness related to sun exposure while using AHAs without proper protection
- Redness
- Itchiness
The FDA noted that side effects to AHAs have decreased since 2004, which likely means both products and the consumers using them are getting more savvy!
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References for this information:
- Journal of the German Society of Dermatology, July 2012, pages 488-491
- Journal of Drugs and Dermatology, June 2021, pages 695-699
- Clinical, Cosmetic, and Investigational Dermatology, November 2010, pages 135–142
- Clinical, Cosmetic and Investigational Dermatology, 2015, pages 9-17
- Journal of Cutaneous and Aesthetic Surgery, Jul-Sep 2019, pages 158-163
- Molecules, April 2018, pages 1–12
- Chinese Journal of Medical Aesthetics and Cosmetology, 2021, pages 260-263
- Journal of Cosmetic and Laser Therapy, January 2013, pages 21-24
- Journal of Clinical and Aesthetic Dermatology, October 2015, issue 8, pages 21–26
- Journal of Cosmetic Dermatology, February 2021, pages 513-521
- Dermatologic Therapy, July/August 2020, ePublication
- Frontiers in Nutrition, March 2022, ePublication
- Nigerian Journal of Surgery, July-December 2020, Volume 26, Issue 2, pages 122-126
- Journal of Cutaneous and Aesthetic Surgery, Oct-Dec 2012, pages 247-253
- Advances in Dermatology and Allergology, 2013, pages 140-145
- International Journal of Medical, Health, Biomedical and Pharmaceutical Engineering, April 2015, ePublication
- Journal of Cosmetic Dermatology, March 2016, pages 49-57
- Food and Drug Administration, Accessed May 2023, Webpage
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