Throughout your skincare journey, you may have heard that you should be using alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). You may even be incorporating these ingredients into your routine already. AHAs and BHAs can have a powerful transformative effect on skin when used safely and in effective formulations. Whether you’re an AHA/BHA newbie or a seasoned expert, join us for a deep dive into what these ingredients are, how they work, how to choose the best AHA or BHA for your skin type, and how to make sure you’re using them safely and effectively.
Covered in this Peach Skincare Academy:
AHAs and BHAs are both acids that occur naturally or can be created synthetically that provide chemical exfoliation. “Alpha” and “beta” may sound like buzzy terms, but they’re straight from organic chemistry: each describes how far apart the hydroxy (alcohol) group is from the acid group within the molecule—“alpha” means the two groups are one carbon apart, while “beta” means they are two carbons apart.
Used within skincare products, AHAs and BHAs slough away dead skin cells to improve the skin’s appearance. While skin does this naturally, shedding layers every few weeks, this process slows down with age and sun damage—AHAs and BHAs provide a quick exfoliation fix (among other benefits) to reveal softer, smoother skin on a more immediate basis.
AHAs can be found in nature in sugarcane, sour milk, and sugary fruits. Types of AHAs used in skincare include glycolic acid, lactic acid, citric acid, malic acid, tartaric acid, and mandelic acid. Of these, the most common (and the most well-researched) is glycolic acid. We covered each type of AHA in our last Peach Skincare Academy: read more.
BHAs, on the other hand, may be found in plants like willow bark, sweet birch, and wintergreen oil. While there are a few different types of BHA ingredients recognized by the FDA for cosmetic use, including tropic acid and trethocanic acid, the most common BHA is salicylic acid. So common, in fact, that salicylic acid is practically synonymous with BHA when it comes to skincare. (Technically, salicylic acid is not a true BHA from a chemist’s perspective because the carbons are on an aromatic benzene ring which gives it different properties than a beta hydroxy acid, but because it’s so popularly referred to as a BHA, the FDA recognizes it as one in cosmetics.)
AHAs and BHAs both provide the same overall benefit when applied topically: they remove dead skin cells so that newer, more evenly pigmented, smoother skin cells regenerate. The process by which each type of acid does this is different, however.
AHAs are water-soluble, so they are only able to work on the surface layer of the skin. They do a lot of great work on that surface layer though! AHAs exfoliate dead skin cells by breaking down the proteins that bind those cells together—if you’ve come across the term “ungluing” in reference to AHA exfoliation, that’s this process. While this was the generally accepted scientific theory for how AHAs exfoliate the skin, the exact mechanism of action wasn’t known until a 2012 study on glycolic acid found that an overload of calcium ions inside skin cells causes them to die and increases cell turnover.
BHAs, meanwhile, are oil-soluble. BHAs are able to penetrate deeper into the skin than AHAs are: they’re able to break through the skin’s oil barrier and get into pores. BHAs work by dissolving oil within pores—this is what helps them effectively break down dead skin cells and sebum, the fatty substance that clogs pores, creates the “slick” appearance of oily skin, and causes breakouts.
Thanks to the exfoliation process kicking your skin into new cell turnover gear, you’ll achieve the same general fresh-faced effect whether you choose an AHA or BHA to incorporate within your skincare routine.
AHAs and BHAs both:
- • Remove dead skin cells from the skin
- • Diminish the appearance of fine lines and surface wrinkles
- • Smooth out skin texture
- • Even out skin tone
- • Help treat acne
- • Reduce the appearance of large pores
Based on your skin type and your goals, you may want to choose one type of acid over another. Because of the properties of each, you’ll receive a unique set of skin benefits when you choose an AHA or a BHA.
- • Provide a moisturizing effect to the skin
- • Improve photoaging markers from sun damage
- • Treat hyperpigmentation and melasma
- • Promotes the skin’s collagen production
AHAs are ideal for people with normal to dry skin types because they have natural humectant properties that attract moisture from deeper layers of the skin (and sometimes even the air)
- • Treat oily skin problems like blackheads and whiteheads
- • Possess anti-inflammatory properties
- • Have anti-microbial properties
BHAs are ideal for people with oily, combination, or acne-prone skin because of their ability to break down sebum within pores.
Salicylic acid is also suited to those with rosacea and other inflammation-related sensitive skin issues—it’s from the same family of compounds as the acetylsalicylic acid in aspirin, so it can help to calm inflammation.
Can I use both?
You can absolutely choose to use a combination of AHAs and BHAs in your skincare routine, should you wish to reap the benefits of both acids.
While you may wish to experiment and find the mixture of products and a schedule that’s right for you, we recommend starting with formulations that include both ingredients. Exfoliating formulas that include both AHAs and BHAs have been calibrated with concentrations, pH levels, and additional helper ingredients to deliver a safe, effective at-home chemical exfoliation. At Peach & Lily, our Super Reboot Resurfacing Mask and The Good Acids Pore Toner combine glycolic acid and salicylic acid at gentle and effectual concentrations for regular home use.
There are a few things to consider as you’re searching for the right AHA and/or BHA product for your skin type and goals:
- • Acid type
- • Concentration amount
- • Formulation
When choosing a specific type of AHA, consider the size of the molecule. The smaller the molecule is, the better it is able to penetrate into the skin’s surface layer.
Glycolic acid is the smallest molecule of the skincare AHAs, so it’s able to get deeper into the top layer than the other types. This is one of the reasons why it’s such a skincare staple for exfoliators—it’s an extremely effective skin penetrator.
The larger water-soluble AHA molecules are not able to penetrate as deeply, so they tend to be gentler on skin. If you are looking for a more immediate effect, the larger molecules may not be for you; however, if your skin is veering toward the sensitive side of normal to dry, look for these larger molecules like lactic acid.
As mentioned above, you’ll most likely encounter salicylic acid when seeking out a BHA for your skincare routine—as it will be very rare to come across another BHA type, your main decision factor will be based instead on concentration and formulation.
Because of their powerful exfoliation capabilities and potential to cause sensitivity, AHAs and BHAs should be formulated at specific concentrations for at-home use—and for AHAs, pH levels need to be balanced as well to help at-home users avoid irritation and skin damage.
Concentration of AHAs
The Cosmetic Industry Review (CIR) Expert Panel, a self-regulatory industry safety review board, found that glycolic and lactic acids are safe for regular at-home use at:
- • Less than or equal to 10% acid concentration
- • 5 or greater pH within the final product
- • Formulations designed to avoid increasing sun sensitivity (or directions provided for daily sun protection use)
Products with concentrations of glycolic or lactic acids higher than 10% are able to be safely used on a brief, discontinuous basis with thorough rinsing or application from a trained professional—with additional sun protection afterward. Our Super Reboot Resurfacing Mask contains 10% glycolic acid, the just-right amount for gentle, safe, effective home use that doesn’t significantly increase sun sensitivity (although we always recommend wearing adequate sun protection!)
Concentration of BHAs
While BHAs have less potential for irritation and sensitivity issues than AHAs, they are still powerful deep exfoliators—wart treatments contain salicylic acid concentrations of 10% to 40%—so you’ll want to look for far lower concentrations of salicylic acids in your products. The FDA does not suggest a specific concentration for home use, but over-the-counter acne treatments are typically 5% of less.
Based on clinical tests examined within an ingredient safety review by the CIR Expert Panel, 2% salicylic acid concentration causes minimal cumulative irritation, while lower concentrations cause slight or no irritation to skin.
Studies have shown that application even on a daily basis of 0.5% salicylic acid formulations have resulted in no skin irritation. At Peach & Lily, Super Reboot Resurfacing Mask and The Good Acids Pore Toner are formulated with low concentrations of 0.5% salicylic acid for gentle pore-clearing action that won’t irritate your skin.
As discussed above, pH levels in AHA formulations are crucial to a balanced product that effectively exfoliates without irritation. But there’s more to a great acid formulation than pH levels. The other ingredients within the formula can help acids do their jobs.
While AHAs have natural humectant properties that help draw moisture to the molecule like a magnet and bring your skin’s moisture to the surface (even attracting moisture from the air around you), sometimes—particularly within especially dry weather or environments—humectants can attract too much moisture and cause more dryness. Look for formulations that include occlusive ingredients that create a protective lipid seal over the skin and prevent the loss of moisture. (Our Super Reboot Resurfacing Mask uses rosemary leaf extract and chamomile extract as occlusives.)
With both AHAs and BHAs, there are certain safety issues that mean you will want to take precautions when using these chemical exfoliants.
- • Sun sensitivity – Be sure to wear sunscreen when using these surface-level exfoliators. Many studies, including those by the FDA, have confirmed that AHA application can lead to increased UV sensitivity.
- • Mixing too many strong acids – While you can combine AHAs and BHAs within your routine, we recommend steering clear of using them on the same day, which can cause over-exfoliation and irritation. We suggest alternating the days on which you use each type—unless, of course, you’re using a product that has already done the work of mixing them in appropriate concentrations for your skin, like our Super Reboot Resurfacing Mask or The Good Acids Pore Toner.
Do you need to avoid certain ingredients when using AHAs or BHAs?
You may have read that you should not mix AHAs or BHAs with products containing retinol, Vitamin C, Vitamin A, or other ingredients.
However, studies show the following combinations work safely (and sometimes even more effectively) together:
- • Glycolic acid and retinols
- • Glycolic acid and vitamin A
- • Glycolic acid and vitamin C
- • Salicylic acid and retinols
- • Salicylic acid and vitamin A
Keep in mind that research is conducted in a clinical setting rather than at-home use. For safe use at home, we recommend slowly introducing ingredient pairings, alternating treatment days and times and keeping an eye out for any irritation, stopping use if you spot any.
Are AHAs & BHAs safe for use during pregnancy and/or breastfeeding?
While no studies have been conducted specifically on the safety of topical AHA or BHA use during pregnancy and breastfeeding, you may have seen reports that you should avoid glycolic acid and salicylic acid during these times due to adverse reproductive effects. The studies that found adverse reproductive effects with these AHA and BHA types, however, were administered in far higher dosages orally than would be applied topically.
Because low amounts of glycolic acid and salicylic acid are absorbed systemically through the skin from topical application, most research suggests that topical application of glycolic acid and salicylic acid should not be of concern during pregnancy.
While breastfeeding, avoid application of salicylic acid and glycolic acid to any area of the body that may come in direct contact with your infant’s skin or mouth, but otherwise these ingredients should not pose concerns to those who are breastfeeding.
Now that you’re an AHA and BHA expert, we’re sure you’d like to try some safe and effective versions in your skincare routine. At Peach & Lily, our founder, Alicia, struggles with eczema and very sensitive skin, so our exfoliators are formulated to be gentle enough even for those with sensitive skin issues.
We have two superstar exfoliators in our lineup:
- • Super Reboot Resurfacing Mask – With a combination of 10% glycolic acid and 0.5% salicylic acid, our Super Reboot Resurfacing Mask is a powerful combination of AHAs and BHAs that’s suitable for regular at-home use even for sensitive skin types. You’ll feel as if you’re getting a professional-grade facial without irritation thanks to our infusion of aloe, green tea, cica, chamomile, and panthenol that soothes and calms skin during the exfoliation process—and you’ll achieve that fresh-faced glow with turmeric and licorice for brightening (they’re also great skin soothers!) While Super Reboot is gentle and safe, we recommend starting low and slow and building up your AHA and BHA tolerance. Very sensitive skin types should start with about 5 minutes once a week and build up to 20 minutes about twice a week, while normal, oily, and dry skin types should start at about 15 minutes once or twice a week and add in additional minutes or days as needed.
- • The Good Acids Pore Toner – Our pH-balancing toner provides gentle daily pore control with a blend of low concentrations of glycolic and salicylic acid—less than 1% of each to avoid irritation. Formulated to be a gentle everyday exfoliator, The Good Acids works to help clear pores and smooth skin in between Super Reboot masking sessions. We’ve added in turmeric, aloe, allatonin, and portulaca oleracea (a traditional Korean medicinal plant to treat inflammation) to soothe and ease skin as the acids get to work. The Good Acids is a great way to maintain the daily care of your pores without harshness or drying ingredients.
Written By: Amy Geppert
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 Cosmetic Ingredient Review Expert Panel. (2019). Amended Safety Assessment of Salicylic Acid and Salicylates as Used in Cosmetics. https://online.personalcarecouncil.org/ctfa-static/online/lists/cir-pdfs/FR766.pdf
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 Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. Salicylic Acid. [Updated 2018 Dec 3]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK500675/Follow my blog with Bloglovin