What is AHA? The Glowy Benefits of Proper Exfoliation

Medically reviewed by Anna H Chacon, M.D. FAAD
Alpha Hydroxy Acids for smooth skin

AHAs blow all other exfoliation methods straight out of the water.

Wait a second...

That makes alpha hydroxy acids sound pretty intense, but the reason we love them so much is because they’re not.

Unlike physical scrubs (apricot pits, cleansing devices, loofahs, etc.) that randomly scratch your skin, too much in some places and not enough in others, AHAs exfoliate the skin by gently breaking up the adhesion of dead cells to healthy cells. They do so in a way that preserves the health and integrity of the skin.

Instead of removing dead cells directly by force, AHAs like glycolic and lactic acid encourage your skin to let go of those dead skin cells all by itself.

They’re kind of like your smartest friend - the one who'll tell you to dump that loser boyfriend or purge your closet of ill-fitting college T-shirts. The only difference is that with AHA, the skin always listens to the good advice.

Plus, AHAs have a few other benefits - namely, they lead to supple, hydrated, glowy, and wrinkle-free skin. Basically, what we all want.

So in this post, we’ll cover this friendly, intelligent category of acids in detail. We’ll explain how they work on a deeper level, cover their wide range of benefits and the science behind them, and give you some tips for incorporating an AHA into your own routine.

    What’s AHA, anyway?

    AHA stands for alpha hydroxy acid, which is a category of water-soluble chemical exfoliants.

    Before you run away from AHAs because they’re “chemicals,” remember that water is a chemical. Heck, your body is made of chemicals! Chemicals are just any pure substance with a “defined” composition.

    Other chemicals you encounter in your day-to-day life include the oxygen you breathe, the salt on your table, and the vitamin C in your fruits, veggies, and maybe even skin care. AHAs are very specific and gentle chemicals that happen to be exactly what the surface of your skin needs to renew itself.

    Exfoliation, of course, is the process of removing dead skin cells from the very surface of the skin. It’s essential for maintaining skin smoothness, improving hydration, and helping leave-on skincare products penetrate into the skin.

    There are a lot of AHAs out there. If you’re into skincare, chances are you’ve heard about glycolic and lactic acids, which are the two main AHAs used in skincare.

    Glycolic Acid

    Glycolic acid has been used in skincare for decades. It’s almost up there with retinol for its incredible effect on skin smoothness, texture, and luminosity, and yet, it doesn’t get nearly the level of adoration it deserves.

    When it comes to skin impact, it’s the smallest of the AHAs and therefore also the most intense (but not too intense, as we’ll get into soon). In skin care, tiny is mighty.

    Smaller molecules penetrate the surface of the stratum corneum with ease (that’s the outermost layer of the epidermis, which is composed entirely of dead skin cells). This allows them to act on the skin more deeply and thoroughly.

    As we’ll soon discuss in more detail, it has been extensively researched not just for its exfoliative power, but also for its ability to slow visible skin aging and amplify the renewing power of retinoids.

    Lactic Acid

    Lactic acid is the gentler of the two main AHAs, thanks to its slightly larger molecular structure. While it’s not quite as potent or exfoliative as glycolic acid, it’s skin-identical. That means that it naturally exists in human skin (especially when we’re young). It helps to keep the skin moist while also aiding with the natural desquamation (i.e. cell-shedding) process.

    It’s often recommended for those with sensitive skin, but we find that combining glycolic and lactic acids provides the skin with a more diverse exfoliative footprint. It’s an ideal way of enhancing the exfoliation abilities of a formula without resorting to levels of glycolic acid that could irritate sensitive skin.

    Alpha hydroxy acid benefits

    What does AHA do for the skin, exactly? AHAs have a few excellent benefits, which we’ll explain here. They exfoliate in a very unique way, which allows them to smooth the skin, reduce wrinkle severity, improve skin moisturization, and optimize skin cell function.

    Thorough and precise exfoliation

    The coolest thing about AHAs is that they exfoliate dead skin cells and ONLY dead skin cells. Glycolic and lactic acids work by loosening the connectivity of the dead skin cells at the very top of the stratum corneum.

    They help those dead skin cells shed on their own in an even and comprehensive way, meaning that your entire face gets equal treatment.

    And why would you want to exfoliate? There’s no better way to speed up skin renewal than by letting go of the old. This is particularly true if you’d like to fade any visible imperfections, but it also helps with nearly every other concern imaginable.


    The secret to AHA’s gentleness is its preciseness. Unlike physical scrubs that scratch the skin in irregular patterns, AHAs tell dead skin cells to shed on their own, in a much more natural and skin-preserving process.

    A well-formulated, low-percentage AHA product will only target old, haggard, and unhelpful dead skin cells. After all, the purpose of exfoliation is to remove the unnecessary dead skin cells - not the entirety of the stratum corneum.

    A three-week study showed that at low percentages, AHA is a gentle exfoliation method that doesn’t irritate or disrupt the skin barrier.

    Supports your anti-aging efforts

    If anti-aging is your goal, your skincare routine should prioritize increasing the skin cell turnover rate. That’s the rate at which skin cells regenerate, and it’s fundamental to encouraging better production of the proteins that keep the skin looking firm.


    The gold standard ingredient for encouraging skin cell turnover is retinol (especially in its enzyme-activated form, retinal), but AHAs pull their weight too. Research shows that both glycolic and lactic acid can improve collagen production, to rejuvenate and reverse signs of photodamage. Pair them with retinol and the results are even more impressive, although as Dr. Anna Chacon reminds us, it’s important to do so carefully to avoid irritaiton. At the beginning, we recommend using them on alternating nights to see how your skin responds. 

    Hydrate directly

    We’re kind of obsessed with water. Keeping the epidermis hydrated maintains the integrity of the skin barrier. It also keeps the skin looking and feeling great - no one likes that tight, dull feeling when the skin is dehydrated!

    People often worry that chemical exfoliants will increase TEWL (transepidermal water loss). But they don’t!

    Both glycolic and lactic acid are humectants, meaning that they’re able to deliver water to the epidermis very directly.

    Sodium lactate, the neutralized form of lactic acid, is actually a pretty common moisturizing agent, but because it’s neutralized, it doesn't exfoliate.

    By using lactic and glycolic acids, you basically get a two-in-one. As you exfoliate your skin, you also get to benefit from their water-absorbing ability… Especially if you use your AHA product in a humid setting like a steamy (but not too hot) shower.

    That said, overusing AHAs or choosing formulas with more than 10% could potentially damage the skin’s barrier functions, and that could lead to moisture loss. Later on, we’ll give you some tips on how to introduce AHA in a way that will preserve the integrity of your skin barrier.

    Primes your skin to hold water

    So we talked about short-term, direct hydration, but what about the long-term? With regular use, AHAs improve your skin’s ability to hold water.

    The three-week study we mentioned above showed that even with twice daily use, glycolic acid did not increase water loss. Another study showed that over a six-week period, both lactic and glycolic acid actually managed to improve skin hydration levels.

    The reason for this, we think, is pretty simple. As excess dead cells are removed, the skin is basically primed to accept and hold more water for increased hydration. Suddenly, there’s room for the fresher layers of your stratum corneum to soak up moisture and expand, not to mention that hydrating products have an easier time seeping in.

    Additionally, AHAs have been found to boost the skin’s renewal mechanisms. One of the positive outcomes of that, along with increasing collagen, they also increase the skin’s natural levels of hyaluronic acid, the ultimate humectant and rejuvenating agent.

    It’s ironic: Proper chemical exfoliation increases skin hydration, while aggressive physical exfoliation actually decreases it.

    Who is AHA best for?

    All skin types can benefit from AHA, but it’s particularly great if your skin needs that exfoliative boost. Those with dry or dehydration-prone skin may benefit the most since AHA also promotes better skin hydration.

    Those with oily skin can also benefit from its thorough exfoliating effect. Because AHA is water-soluble rather than oil-soluble, its cousin beta hydroxy acid (BHA or salicylic acid) is often recommended instead. But the two ingredients work beautifully together. You can rely on AHA for surface exfoliation, while BHA works more deeply within the pores.

    Finally, there’s sensitive skin. Some people with sensitive skin truly cannot tolerate any exfoliation, but more often than not, the issues come from using an AHA that’s way too aggressive. Concentration really matters, and more isn’t better.

    Studies show that at very high concentrations, the benefits of using AHA diminish while risks grow. On the other hand, using low-percentage AHA on a regular basis provides optimal benefits.

    Besides concentration, it’s also important to take pH into account. A pH below 3.5 can be quite harsh and only makes sense in a professional setting. AHA exfoliants with a pH between 3.5 and 4 are at the sweet spot where they exfoliate well but without causing irritation.

    AHA and Dark Skin

    There’s a mistaken idea floating around that those with deeper skin tones can’t use AHA. This is not true.

    Those with deeper skin tones are more likely to experience hyperpigmentation as a response to trauma and inflammation, so issues have cropped up with peeling solutions that contain a high percentage of acids. However, gently-formulated products with 10% AHA or less are perfectly fine as long as you listen to your skin, don’t overdo it, and use sun protection.

    But Don’t Use AHA If…

    You don’t use sun protection. Some people hate the texture of sunscreen, others are just forgetful. We’re not here to sunscreen shame you, but if this essential skin protective measure isn’t part of your routine yet, then AHA can wait.

    Choosing a daily AHA

    Your go-to AHA shouldn’t be too harsh, especially if it’s your first time using this ingredient, or if you’ve over-exfoliated with it in the past.

    Opt for a 5% to 10% formula, and make sure the pH is between 3.5 and 4. Any higher and it won’t be effective, while any lower and it won’t be gentle. Stay away from brands that don’t disclose this important information!

    We’ve tailor-made our Double Alpha Hydroxy Cleanser to provide the right level of exfoliation across skin types. It has a pH of 4, which is at the perfect cusp of being as gentle as possible while still allowing the AHAs to do their job.

    Because it’s formulated as a cleanser, those with sensitive skin can use it for short “contact therapy” to get a mild exfoliation without pushing their skin too hard.

    The viscous gel formula isn’t too watery or surfactant-heavy, but it rinses away with ease. You can even achieve a dramatic exfoliation by using it just like a peel a few times a week.

    How to use AHA

    How you use your AHA product depends on how it’s formulated. Serums and toners can just be applied and left on the skin, while AHA cleanser and peels should be applied and then rinsed off. You can even use AHA cleansers and lotions on your body, for truly next-level all-over exfoliation!  

    One rule to remember, no matter which AHA product you use, is that it needs to come in contact with your skin early in your skincare routine steps. Active skincare products are best applied from most acidic to least acidic, and AHAs tend to be quite acidic (along with BHAs and vitamin C).

    Step-by-step guide

    1. Rinse your face with water. If you’re using a leave-on AHA, cleanse your face as well.
    2. Gently smooth your AHA product over the skin without rubbing. We always recommend applying it with your hands, even if you’re using a toner. It may tingle a little - that’s normal at first.
    3. You can localize your application to parts of the face that need more care, like the T-zone ( i.e., the forehead, nose, and chin), but we recommend treating the entire face.
    4. Wait anywhere between 30 seconds and up to 30 minutes depending on the specific product you’re using. The longer you leave your product on, the more dramatic its exfoliative effects will be.
    5. Finally, if you’re using a rinse-off product, splash your face with cool water to remove it. If not, just proceed with the rest of your routine.

    Tips for introducing AHA safely

    If it’s your first time (or your first time in a long time) using glycolic or lactic acid, keep these tips in mind.

    • Make sure that you’re already using sunscreen and following other sun protection habits before you start using AHA.
    • Introduce AHA into your routine slowly, only using it a few times a week. During that early period, pay close attention to how your skin responds to it.
    • Listen to your skin, and pay attention to any signs of over-exfoliation like dryness, flakiness, redness, or tenderness. This is more likely to occur with more intense AHA products.
    • With regular use, your skin cell turnover rate will increase, which thickens and reinforces the skin barrier. Within a few weeks, you’ll be able to increase the frequency up to once a day (some people even use it twice a day safely, but we think that’s overkill).
    • If your skin is sensitive, you may find that exfoliating just a few times a week works best for your skin, and that’s okay too!

    Don’t forget sunscreen - really!

    The only drawback to AHA is that it makes the skin more sensitive to sun exposure, likely because of just how thoroughly it exfoliates. This photosensitivity occurs no matter when you use AHA.

    So while you’re using any AHA product, day or night, practice sun protection like your life depends on it. If you stop using AHA for a week, your skin will go back to its normal resilience.

    If you’re very forgetful and often find yourself experiencing direct, unprotected sun exposure, you might be better off avoiding AHAs altogether.

    Have your AHA moment

    The thing that makes AHA so mind-blowing is that it exfoliates as though it were intelligent. It doesn’t “melt dead skin cells” or scratch them off. It tells them to shed, enhancing an essential skin behavior that often malfunctions as we get older.

    But using AHA can be irritating, especially when it comes to formulas with a very high percentage of glycolic acid or a very low pH. Those intense peels can break down the skin’s barrier functions, whereas gentle formulas will actually reinforce it.

    But as long as you choose a gentle, friendly AHA, expect your skin to thrive.

    Medically reviewed by Anna H Chacon, M.D. FAAD

    Try a Retinol with Guaranteed Results

    Is your retinol not yellow?

    That's the first...yellow flag that your retinol may not be formulated properly. Real retinol––like it's cousin beta carotene that makes carrots bright orange––should be bright yellow.