Out with the old, in with the new—in short, that’s what chemical exfoliants do! In skincare, chemical exfoliation often describes the process by which hydroxy acids remove dead skin cells and help speed up the skin’s cell turnover rate. This helps improve the complexion, brighten the skin, and fade hyperpigmentation. Small molecules penetrate the skin, working to slough off dead cells from the skin’s surface, smooth roughness, and lessen the appearance of fine lines and wrinkles.¹ Two common types of hydroxy acids are AHAs (alpha hydroxy acids) and BHAs (beta hydroxy acids). AHAs are water-soluble, while BHAs are oil-soluble. Knowing which one works best for you depends on your skin type—especially if you have sensitive skin. 

Let’s dig into the various types of AHAs, AHAs versus BHAs, the best AHA for sensitive skin, and skin purging.

AHAs vs. BHAs: What’s the difference?

In general, AHA skincare products are ideal for dry skin because they work in the skin’s superficial layers. “They ‘unglue’ dead skin cells,” says Elise Griffin, a licensed physician assistant at Curology, “allowing them to shed more easily to improve dry, flaky, dull skin and clogged pores.” They may cause skin sensitivity and should ideally be used in the evenings. A broad-spectrum sunscreen with SPF 30 should be used in the morning. AHAs can help address the following skin concerns:²

• Photoaging

• Hyperpigmentation

• Uneven skin tone

BHAs, on the other hand, usually work well on oily skin, as they “degunk” pores and work on a deeper level than AHAs, in addition to helping reduce inflammation. While they can be drying, they are not known to cause sun sensitivity, so they’re generally safe to use as part of your morning or nighttime skincare routine. BHAs can help treat the following: 

• Acne

• Fine lines and wrinkles 

• Inflammation 

• Skin texture

In short, if you’re seeking anti-aging benefits and have dry skin, try an AHA. If tackling acne is on your to-do list, go with a BHA. Either way, it's important to not overdo it. Too much chemical exfoliation can be rough on your skin, especially if you have sensitive skin.

Types of AHAs 

While all AHAs offer some serious exfoliation, knowing the differences between the types of acids is key since the effects and uses can vary between them. Remember that exfoliation can make your skin more sensitive to the sun, so always wear your SPF! Although this list is not complete, here are some common types of AHAs: 

• Glycolic acid. A common AHA, glycolic acid is antimicrobial, highly exfoliating, and can help to treat acne breakouts.³ You can find it in many skincare products, including toners and peels.

• Lactic acid. Another common AHA, lactic acid is a chemical exfoliant that has been shown to potentially improve skin firmness, thickness, and texture, as well as reduce the appearance of lines and wrinkles.⁴ It can be found in many products, but lactic acid peels are particularly popular. 

• Citric acid. A naturally occurring substance found in citrus fruits, citric acid may smooth the skin and reduce signs of aging when applied topically. Research shows that it has the potential to reverse signs of photodamage by increasing collagen synthesis and improving the quality of elastic fibers.⁵

• Mandelic acid. Mandelic acid has larger molecules than many AHAs and has anti-inflammatory properties.⁶ It has the potential to treat hyperpigmentation and acne and improve skin quality and is typically well-tolerated.⁷ 

Which AHA is best for sensitive skin?

While there’s no best chemical exfoliant for sensitive skin, some are better suited to it than others. “Mandelic acid tends to be the most gentle and is not as potentially irritating as lactic or glycolic acid,” says Donna McIntyre, a nurse practitioner at Curology.

If you have sensitive skin, we suggest starting with a low-strength AHA. Use it one to two times weekly and increase the frequency as your skin becomes more tolerant to it. Mandelic acid’s larger molecule size makes it likely to be better tolerated than some of the other AHAs. 

What is skin purging? 

Skin purging can happen as your skin adjusts to certain new active ingredients. That’s typical because these active ingredients work to speed up cell turnover and slough off dead skin cells—which also loosens congestion deep inside the skin, pushing it up to the surface. The resulting “purge” is often seen as microcomedones (blackheads and whiteheads). Purging can occur anywhere on the face, and you may also notice dryness and peeling as your skin adjusts to the active ingredient.

Generally speaking, AHAs don’t cause purging, but of course, everyone’s skin may react differently. It’s more common with other ingredients like tretinoin and azelaic acid. 

Is it skin purging or acne?

Not every reaction to a new product is skin purging, and there are a few ways to differentiate between skin purging and acne breakouts. It’s also important to always consider if your new skincare product may irritate your skin for reasons other than skin purging, such as an allergic reaction. 

Take the guesswork out of your skincare with Curology

Ready for an AHA moment in your skincare routine? If so, your Curology dermatology provider can help you determine which to try based on your skin type and skin goals when you sign up for a free consultation. Just upload selfies with updates periodically so they can monitor for any possible signs of irritation. The trial-and-error process is a delicate but necessary part of your unique skincare journey, and we’re here for you every step of the way.

Get your personalized skincare routine with Curology

Get your personalized skincare routine with Curology

Start your skin quiz

Not yet a member? Getting started is easy. Best of all, your first month of Curology is on us—just pay $4.95 (plus tax)* to cover shipping and handling, and we’ve got the rest. You’ll receive your personalized prescription formula designed to target your specific skin concerns at no extra cost, and your dermatology provider will include other Curology products that they think will help take the guesswork out of skincare.

P.S. We did the homework so you don’t have to:

1. Moghimipour, E., Hydroxy Acids, the Most Widely Used Anti-aging Agents. Jundishapur J Nat Pharm Prod. (2012).

2. Moghimipour, E., Hydroxy Acids, the Most Widely Used Anti-aging Agents. Ibid.

3. Christoph, Prof. Dr. med. A., et al,  A 10% glycolic acid containing oil-in-water emulsion improves mild acne: a randomized double-blind placebo-controlled trial. Journal of Cosmetic Dermatology. (2011).

4. Smith, W.P. Epidermal and dermal effects of topical lactic acid. J Am Acad Dermatol. (1996).

5. Citric acid: An α and β hydroxyacid for antiaging. Journal of the American Academy of Dermatology. (2005).

6. Garofalo, V., et al. Clinical evidence on the efficacy and tolerability of a topical medical device containing benzoylperoxide 4%, retinol 0.5%, mandelic acid 1% and lactobionic acid 1% in the treatment of mild facial acne: an open label pilot study. Clin Cosmet Investig Dermatol. (2019).

7. Jacobs, S.W., Culbertson, E.J. Effects of Topical Mandelic Acid Treatment on Facial Skin Viscoelasticity. Facial Plast Surg. (2018).

Donna McIntyre is a board-certified nurse practitioner at Curology. She obtained her Master of Science in Nursing at MGH Institute of Health Professions in Boston, MA.

* Subject to consultation. Subscription is required. Trial is 30 days. Results may vary. 

Written by

Curology Team

Medically reviewed by

Donna McIntyre, NP-BC