An introduction to alpha hydroxy acid (AHA), its benefits, side effects, and best products
Alpha hydroxy acids, or AHAs, are popular ingredients in skin care products for acne, anti aging, or just general moisturizers, but rarely do these products also educate you about how to safely use an AHA, the benefits they offer or their side effects. AHAs are potent and if you use them without proper care for your skin, they can result in more damage than their intended benefits. AHAs also can help deal with a wide range of skin problems, from hydration to pigmentation and scars to acne to sun damage and aging. This guide explains the benefits, side effects, different types of alpha hydroxy acids, and offer some recommendations for best performing AHA products for skin problems.
What is AHA or alpha hydroxy acid?
Alpha hydroxy acid, or AHA, is 1 of 2 hydroxy acids that is commonly used in cosmetic products for exfoliation, hydration. They’re especially popular in anti aging skincare products. AHAs can be synthetic created or naturally derived from fruit, nuts, sugar or dairy products. The other common hydroxy acid is beta hydroxy acid or bha. To learn more about bha, read our guide to bha or beta hydroxy acids here.
Unlike beta hydroxy acids which are oil soluble, alpha hydroxy acids are water soluble and so cannot penetrate the skin like beta hydroxy acids. This makes them great for aged skin (like thickened skin) or sun damaged skin that doesn’t have acne issues. Alpha hydroxy acid is very potent in deal with the skin at the surface. AHA exfoliates the top layers of skin by breaking the bonds between outer layer skin cells, sloughs off dead skin and reveals new undamaged skin underneath.
It is also hydrophilic (attracts water molecules) and helps skin retain more water and feel bouncy and hydrated.
Alpha hydroxy acid makes your skin much more sun sensitive. So if you want add an AHA to routine, you MUST add a sunscreen. Otherwise you’ll be exfoliating to get new undamaged skin only to damage the young skin further with sun exposure.
We cannot stress this enough: If you want to use an AHA, PLEASE USE SUNSCREEN! Otherwise you risk even more damage to your skin than if you had not used an alpha hydroxy acid at all.
Alpha hydroxy acids are available in a variety of concentrations, from 1% to 50% and even higher, that are proportionally stronger exfoliants. But, you have to build up your skin’s tolerance from a lower to high concentration or you can risk over exfoliation, which is difficult to repair and can take weeks or even months.
Alpha hydroxy acid helps speed up the process of removing dead skin and the topmost layers of skin. This doesn’t happen overnight, but AHA helps speed this process. This results in bringing new skin to the surface that looks bright and full. So alpha hydroxy acid is a common product in products that help fight fine lines, wrinkles, other signs of aging, and in products that help reduce hyperpigmentation, acne scars, and sun damage. Thanks to AHA’s water attracting properties, it also helps improve and condition dry skin. Routine use of an AHA over time can result in smoother, more hydrated, and firmer skin.
What are the benefits of AHA?
Alpha hydroxy acids offer a number of benefits, but how many of them are backed by science. Let’s take a look at some of the main benefits of AHAs.
How does AHA treat acne?
As alpha hydroxy acid breaks the bonds between skin cells and helps speed up exfoliation, it can also open up or loosen clogged comedones that are at or near the surface of your skin. Studies show that AHA is effective in treating mild or moderate acne or helping maintain against future breakouts after a stronger acne treatment.
In one study, 248 patients with mild to moderate acne in Italy were prescribed Hyseac AHA cream to be applied twice a day for 60 days. These patients had comedonic acne, inflammatory acne or a combination of both. The results of that study:
The tolerability was good to excellent in 92.3% patients, without significant differences between patients using AHA cream in monotherapy (90.0%) or associated with concomitant pharmacological treatment (97.6%). The efficacy was overall high in 64.2% patients, again without significant differences related to concomitant pharmacological treatment or not (64.8% vs. 63.3%) and/or the acne clinical type (comedonic vs. inflammatory vs. mixed: 69.2% vs. 66.7% vs. 58%). [source: Baldo A1, Bezzola P, Curatolo S, Florio T, Lo Guzzo G, Lo Presti M, Sala GP, Serra F, Tonin E, Pellicano M, Pimpinelli N. (2010) G Ital Dermatol Venereol]
Most of these patients saw an improvement in their acne, no matter what type of ache they had, and no matter how the AHA was prescribed for them to use, on its own or with another treatment.
AHA for hyperpigmentation?
AHA has also been shown to reduce acne scars, post inflammatory hyperpigmentation (PIH), sun damage spots and other skin discolorations. This is thanks to how AHA speeds up exfoliation at the skin surface level.
In one study, 7 Indian patients with darker skin (Fitzpatrick skin type IV-V) and acne scarring were treated with lactic acid, an alpha hydroxy acid, every 2 weeks for up to 2 months total. These patients were monitored for 3 months after the end of the treatment as well to ensure that the perceived effects of the peels were not just short term. How did it turn out?
At the end of 3 months, there was definite improvement in the texture, pigmentation, and appearance of the treated skin, with lightening of scars. Significant improvement (greater than 75% clearance of lesions) occurred in one patient (14.28%), good improvement (51-75% clearance) in three patients (42.84%), moderate improvement (26-50% clearance) in two patients (28.57%), and mild improvement (1-25% clearance) in one patient (14.28%). [source: Sachdeva S. (2010) J Cosmet Dermatol]
Another study involved a group of 33 older female patients with a mean age of 55.5 years and moderate to severe sun damage on their hands, like age spots, freckles and other discoloration. These patients’ hands were treated twice daily for 8 weeks with a topical cream formulated of an alpha hydroxy acid, anti oxidants, and depigmenting agents. The results:
Thirty-five subjects were enrolled with a mean age of 55.6 years; 33 subjects completed the study. The IGA of the appearance of hand photodamage improved from a mean (standard deviation) score of 5.0 (0.8) at baseline to 3.1 (1.5) and 2.6 (1.3) at weeks 4 and 8, respectively (1=mild; 9=severe). Based on expert-grader evaluation, subjects demonstrated statistically significant improvements from baseline in IGA at weeks 4 and 8 in age spots and freckling at weeks 4 and 8, (P<.0003) and in skin discolorations at week 8 (P<.05). The majority of subjects reported that they perceived improvements in each of the 9 parameters associated with skin appearance. No adverse events were reported.
The appearance of age-related hand pigmentation characteristics were significantly improved at 4 and 8 weeks of treatment. Subjects reported post-treatment improvements in other characteristics associated with healthy skin. [source: Gold MH, Gallagher C. (2013) J Drugs Dermatol]
AHA for anti aging
You would guess that using an alpha hydroxy acid to remove the top most layers of skin would result in thin skin, but actually the opposite is true. In addition to AHA’s reversal of age and sun damage and discoloration as evidenced in the previous study, AHAs also help thicken your skin and increase skin elasticity and collagen density. All of these benefits help fight age related skin deterioration, like wrinkles and fine lines.
In the following study, patients applied AHAs to their forearm to measure exactly this and found positive improvements on all fronts:
Alpha-Hydroxy acids (AHAs) have been reported to improve aging skin. The mechanisms of action of AHAs on epidermal and dermal compartments need clarification. Our purpose was to determine the effects of AHAs on photoaged human skin by clinical and microanalytic means. Patients applied a lotion containing 25% glycolic, lactic, or citric acid to one forearm and a placebo lotion to the opposite forearm for an average of 6 months. Thickness of forearm skin was measured throughout the study. Biopsy specimens from both forearms were processed for analysis at the end of the study.
Treatment with AHAs caused an approximate 25% increase in skin thickness. The epidermis was thicker and papillary dermal changes included increased thickness, increased acid mucopolysaccharides, improved quality of elastic fibers, and increased density of collagen. No inflammation was evident.Treatment with AHAs produced significant reversal of epidermal and dermal markers of photoaging. [source: Ditre CM 1 , Griffin TD , Murphy GF , Sueki H , Telegan B , Johnson WC , Yu RJ , Van Scott EJ (1996) Journal of the American Academy of Dermatology]
How to use an AHA?
Alpha hydroxy acid is an active. This means that it is an ingredient that has a direct and active action on skin. Other actives include beta hydroxy acids (BHA), Vitamin A (retinoids and retinol), and Vitamin C.
There is some discussion in favor and against this, but we believe that for an active to work best, it should be in direct contact with your skin for several minutes before it is washed off or further products are layered on top. This time period lets the active acid make contact and penetrate your skin undisturbed. If you wash it off, you may not have left it long enough for it act or penetrate completely.
Alpha hydroxy acids also work best in a pH environment between 5 and 6, which is slightly acidic. If you layer on more products on top of your AHA too soon, you may change the pH environment of your skin and not allow the AHA enough contact time to work as well and make it less effective.
With many AHAs that have a higher concentration, the directions for use will ask you to gradually increase the contact time over a series of weeks. For example, you only leave the AHA on your skin for a total of 1 minute the first time you use it, 2 minutes the next time, and so gradually work your way up to 4 to 5 minutes over the course of several weeks. The longer you leave it on, the stronger the exfoliation. But if you leave it on for 4 to 5 minutes on your first use, you’ll very likely end up with highly irritated skin that is red, experience painful stinging and burning, and a severe peel that will be difficult to cover up with moisturizer and makeup. I hope that sounds unappealing enough that you will take precautions and be patient with your skin while using an AHA!
If you have never used an alpha hydroxy acid before or do not know how much AHA your skin can tolerate, it is important to patch test. You can apply a drop of the AHA on the inside of your elbow or on your neck in the same way that you would apply it on your face, and see if these areas react negatively. If they do, you now know that the AHA product is not good for your face and may have negative effects.
That’s essentially a summed up explanation of how to use AHA. We’ll write a longer post on this and link it here when it’s ready if you’re interested in real studies that show the effectiveness of AHA wait times in low pHs.
AHA side effects
Alpha hydroxy acids offer a number of amazing anti-acne and anti-aging results for your skin. But they may not work for everyone as there are also a number of side effects.
Alpha hydroxy acid side effects include burning, swelling, stinging, itching, redness, peeling, and skin discoloration.
We all have skins of various thicknesses and various tolerance levels for AHA concentrations. Some may find that they’re only able to tolerate a very low concentration of alpha hydroxy acid and experience dramatic peeling and burning if they try an acid that is higher than their tolerance. Others may find that their skin can tolerate high levels of acid without even minor peeling or irritation. It may take some trial and error to figure out how your own skin reacts to various concentrations.
What’s the difference between AHA and BHA?
You may already gathered the main differences between alpha and beta hydroxy acids, but we’ll go over them once more for clarity.
Oil vs water soluble
Alpha hydroxy acids are water soluble versus beta hydroxy acids which are oil soluble. So alpha hydroxy acids do not penetrate your skin like beta hydroxy acids and instead work at the skin’s surface level to help exfoliate skin by dissolving the bonds between skin cells and shedding dead and topmost skin cells to reveal undamaged skin below. BHAs are oil soluble and work on the skin below surface level. Learn more about beta hydroxy acids with our guide to BHAs.
Unlike BHAs which do not make your skin more sensitive to the sun, alpha hydroxy acids greatly increase your sun sensitivity. Because they exfoliate top layers of skin which are protective, using alpha hydroxy acids can make your skin more vulnerable to environmental damage (like from the sun or pollution).
So it is HIGHLY IMPORTANT that you wear sunscreen if you are going to add an alpha hydroxy acid to your routine. Even some body moisturizers for dry skin or winter weather may have some form of an AHA to aid with skin hydration, so pay attention to ingredients list to make sure none of the common forms of AHA are included in the product. If they are, wear sunscreen (even if the sun isn’t out) if you plan on going outside. Not sure what the common forms of AHA are? We’ll be covering them in the next section so check that out.
Wrinkles and fine lines
Both AHA and BHA help exfoliate your skin and remove sun damaged skin, but AHA does far more. AHA helps thicken your skin, improve skin elasticity, and increase collagen density. AHA also attracts water to your skin. So in addition to speeding up the exfoliation of your top most layers, AHA helps improve your skin in ways that will result in less lines and wrinkles and attract hydration to help your skin look more plump.
Hyperpigmentation and scars
There are several kinds of AHAs and many of them show real results in reducing hyperpigmentation, scars, and other skin discoloration. Repeat and routine use of AHAs help remove layers of damaged skin, reverse acne or sun damage, and studies have shown that pigmentation and scars can be entirely removed with an AHA.
What are the different types of AHA?
1. Glycolic acid
Glycolic acid is derived from sugar and has one of the smallest molecules in AHAs found in skincare. This means it can penetrate deeper than any of the other common alpha hydroxy acids. This makes it one of the strongest AHAs, but also one of the harshest if you’re unable to tolerate this level of AHA strength.
Beginners should probably start their AHA journey with a different & gentler option, like lactic or mandelic acid. For experienced users, glycolic acid is a highly effective AHA that shows excellent results in all of the areas that alpha hydroxy acids are shown to improve for your skin.
2. Lactic acid
Lactic acid is derived from diary and people who report milk allergies should avoid this AHA.
Lactic acid has bigger molecules than glycolic but smaller molecules than mandelic acid. This makes it a gentler AHA that is a great starter acid for most people. It does everything glycolic acid does but because it has bigger molecules, the effects take a little bit longer.
Lactic acid is available in a range of concentrations for topical use. A 2% and above lactic acid concentration will help increase the hydration of your skin and a 5% and above lactic acid solution will also exfoliate your skin. Skincare products that promise exfoliation will normally have a 5% to 10% lactic acid concentration.
3. Mandelic acid
Mandelic acid is derived from almonds, so if you have a nut allergy, I would try a different AHA.
Mandelic acid has bigger molecules than lactic acid so it does not penetrate your skin as fast and also shows effects slower. This makes mandelic acid great for people who have very sensitive skin that is easily prone to rashes and irritation.
Anyone else can use it as well if you’re looking for a routine acid that will help give you a little bit of AHA power in your routine but without needing drastic results immediately.
4. Malic acid
Malic acid is made from apples but can also be created synthetically. The synthetic version is found more commonly than the naturally occurring version in skincare products, because it is easier to stabilize.
Malic acid molecules are larger than glycolic and lactic acid so it penetrates more slowly like mandelic acid. Malic acid is a great supplementary AHA alongside glycolic or lactic at low concentrations, because together they are able to penetrate at different speeds and so affect the skin at different levels.
5. Tartaric acid
Tartaric acid occurs naturally in grapes, but is also made synthetically and like malic acid the synthetic version is used in products that require a more stable acid.
Tartaric acid has a very big molecule, almost double a glycolic acid molecule. While it is able to exfoliate skin, it is used primarily as a pH adjuster to prime the way for a stronger acid like glycolic or lactic acid to go to work. However, in certain products that use AHAs with varying molecule sizes to penetrate to and exfoliate different layers of the skin, tartaric acid may be used to exfoliate the topmost layer of skin.
6. Citric acid
Citric acid is derived from, you guessed it, citrus fruit. But it also is found in berries and other fruit.
Like tartaric acid, citric acid is primarily used as a pH adjuster in skincare formulas that help keep it within a certain range so that other more potent acids have an optimal environment for effectiveness. Citric acid is also used for its antioxidant properties.
Citric acid can be confused with Vitamin C in skincare, but they are two different compounds. Vitamin C is actually L-Ascorbic acid or ascorbic acid, which is similar to but different than citric acid. Vitamin C is also another active but it is not an alpha hydroxy acid. Check out our guide to Vitamin C for your skin here.
AHAs Product Recommendations
If you want to add an AHA to your skincare routine, here are some of our top recommendations for different types of AHAs. Remember, please patch test on the inside of your elbow or your neck before using these on your face.
1. Paula’s Choice Skin Perfecting Gel Exfoliant
The COSRX AHA liquid is an 7% glycolic acid solution in a base of butylene glycol and apple water. It also has other skin conditioning ingredients and is a gentle and well formulated AHA that is great for regular use. This is a leave on AHA and does not need to be washed off.
Read more reviews of COSRX AHA 7 Whitehead Power Liquid.
2. OZNaturals Glycolic Acid Facial Peel
This is a 30% glycolic solution meant to be used as a peel. This means you apply, leave on for a set period of time, wash it off, and then continue with your routine. Because of its higher concentration,
we’ve seen results immediately, namely plumper hydrated skin and increasing brightness during the subsequent days.
OZ Naturals will give you a refund if you try their product and decide that you do not like it within 30 days from purchase
Read more reviews of OZNaturals Glycolic Acid Facial Peel.
3. Paula’s Choice Skin Perfecting Gel Exfoliant
The Skin Perfecting Gel Exfoliant is an 8% glycolic solution by Paula’s Choice. This is a leave on exfoliant. The Gel Exfoliant also includes an ingredient that is a pH adjuster to help maximize it’s efficacy, as well as antioxidants and skin soothing plant extracts.
Read more reviews of Paula’s Choice Skin Perfecting Gel Exfoliant.
1. The Ordinary Lactic Acid 10%
2. Clear Lift Revitalizing Serum
3. Theraderm – Fruit Acid Exfoliant
1. Mandelic acid 5% Skin prep water
2. Makeup Artist’s Choice Mandelic Acid Serum
3. Naruko AMPM Total Brightening Renewal Treatment