AHA or BHA? Pick by purpose, not by percentage.

What is a chemical peel?

A chemical peel is a procedure in which an acid is applied to cause controlled damage to the skin, which then regenerates. It is used for acne, pigment problems and sun-related aging. The deeper the peel reaches, the more visible the result and the higher the rate of complications. [3]

Depth is what separates one peel from another. A European expert review sorts peels into three classes: superficial, medium and deep. [9]

This guide focuses on the AHA and BHA exfoliants you use at home. Professional peels appear only as context: because both results and complications rise with depth, they are a clinician’s decision and a clinician’s job. [10]

AHA vs BHA: what is the difference?

AHA (alpha hydroxy acid) and BHA (beta hydroxy acid) are two classes of hydroxy acids used as chemical exfoliants. The wider family also includes polyhydroxy acids and bionic acids. Their uses range from photoaging and acne to pigment disorders. [11]

The AHA group includes glycolic acid, lactic, malic, tartaric and citric acid. They are common in cosmetic formulas and are also used in dermatology as superficial peeling agents. [1]

In skincare, BHA usually means salicylic acid. It loosens the junctions between cells so the outer layer sheds, and its comedolytic effect (helping dissolve the plug in a clogged pore) is why it is used as a peeling agent for acne-prone skin. [2]

How AHA and BHA compare

Both exfoliate. They differ in chemical class and in what each has mainly been tested for: AHAs for sun damage and texture, BHA for clogging and breakouts. Head-to-head comparisons mostly come from clinic peels.

You will often read that “BHA is oil-soluble, so it gets inside the pore.” The study abstracts we used do not measure this, so we do not present it as a finding here. A systematic review of acne peels also found no clear difference between glycolic and salicylic acid peels. [6]

What do AHA and BHA do for skin?

AHA and BHA products have mainly been studied for signs of sun damage, breakouts and the brown marks acne can leave behind. Controlled trials of low-strength home products are few and mostly small, and some stronger-looking results come from clinic peels. Check which strength was tested, and where.

Sun damage and texture

In a double-blind trial, 74 women aged 40 to 70 with sun-damaged facial skin used 8% glycolic acid, 8% lactic acid or a cream without active ingredient twice a day for 22 weeks. At least a one-grade improvement in overall photodamage was seen in 76% with glycolic acid, 71% with lactic acid and 40% with the plain cream. The authors described the benefit as “modest.” [5]

In another study, 5% and 12% lactic acid were applied twice daily for three months. Both strengths produced similar changes in smoothness and in the epidermis; increased firmness and thickness in the dermis appeared only with 12%. The abstract does not report the number of participants or a placebo arm, so read this as one small study. [13]

Breakouts and blackheads

For leave-on salicylic acid products, the evidence is weak. A Cochrane review rated the evidence from salicylic acid comparisons as low or very low quality and noted that some studies reported peeling and redness. [14]

Clinic peels give a clearer but still limited picture. A systematic review of 12 randomized trials (387 participants) found glycolic acid peels better than placebo and no difference between glycolic and salicylic acid peels. Salicylic acid may work better on comedones (blackheads and whiteheads) than another peel mixture it was compared with: a 53.4% versus 26.3% reduction. Study quality ranged from very low to moderate. [6]

Our blackheads guide explains what is realistic at home. Painful, widespread or scarring breakouts need a dermatologist, not just an exfoliant.

Dark marks and acne scars

For the brown marks left after a breakout or irritation (post-inflammatory hyperpigmentation), a systematic review of 47 studies counted hydroxy acids among the topical agents backed by the most high-quality studies. Nearly every study recommended SPF 30 or higher, and measurement methods varied from study to study. [7]

The dark spots guide helps you tell marks apart, and the acne scars guide explains how a brown mark differs from a pitted scar.

How do you use a chemical exfoliant at home?

An at-home chemical exfoliant is not a scaled-down clinic peel. It means using a low-strength AHA or BHA product regularly and carefully. Start with one new product, follow the label and never skip daytime sunscreen. Do not copy a professional peel with pure acid solutions or online “recipes.”

Products sold online vary widely in strength. In 50 AHA exfoliants found on one e-commerce site, the concentration ranged from 2.5% to 70%; 19 exceeded the recommended level and 12 did not state a concentration at all. [8]

Serum, toner or cleanser?

Serums, toners and cleansers are the most common AHA BHA exfoliant formats, but the home-product trials we reviewed used creams, so we have no separate results for serums or toners. [5, 13] The steps below are general advice, not study findings:

1. Apply to clean, dry skin. Keep away from the eyes and lips.
2. Use a thin layer. A toner on a cotton pad or with your hands, a serum as a few drops.
3. Follow with moisturizer. Rinse wash-off products on time.
4. Wear sunscreen the next morning. The reason is in the sun section below.

What percentage, and how often?

The Cosmetic Ingredient Review (CIR) expert panel recommends no more than 10% AHA in cosmetics. [8] Home-product trials used 8% glycolic or lactic acid and 5–12% lactic acid, applied twice a day. [5, 13] According to one review, whether an AHA helps or harms the skin depends on its concentration; a higher percentage at home does not mean a better result. [1]

No study in our sources tested how often to use an exfoliant at home. As general advice, many people start with a few evenings a week and adjust to how their skin responds. If stinging, redness or flaking appears, cut back or pause.

When to use AHA and BHA together

No study in our sources tested using AHA and BHA in the same product or the same routine at home. Combination products are common, but layering two separate exfoliants on the same evening makes it harder to tell which one caused any irritation. If one acid covers your goal, you do not need to add the second.

If you use retinol, general advice is to use the acid on different evenings and not start both at once; this is untested too.

Why do acids call for sunscreen?

Acid-exfoliated skin can become more sun-sensitive, so sunscreen is a fixed part of any routine with a chemical exfoliant. In a randomized, double-blind study, 29 volunteers applied 10% glycolic acid to their backs for four weeks; after UV exposure, sunburn cells increased and less UV was needed to cause redness. The effect was gone one week after stopping. [4]

The study was small, with only white participants and back skin. Still, the US Food and Drug Administration (FDA) recommends a sunburn warning on AHA cosmetics, yet only 16 of 50 product pages reviewed showed one. [8] Very few studies have examined how long-term hydroxy acid use affects sun-related skin cancer. [11]

After professional peels, sun exposure is also listed among the factors that make complications more likely. [3] As general advice, apply broad-spectrum sunscreen every morning while you use an acid and for the week after you stop. For amount and reapplication, see the sunscreen guide.

Side effects: what should you expect?

The side effects of a chemical exfoliant depend mostly on the acid’s strength and how deep it works. Swelling, burning and itching have been reported with AHA products. [1] With professional peels, complications range from mild irritation and uneven color to permanent scarring and, in very rare cases, can be life-threatening. [3]

Peeling and redness also appear in salicylic acid studies. [14] In the study comparing 30% peels in a clinic, glycolic acid caused more side effects after the first session. [12] In the 22-week home cream trial, only one of 74 women stopped because of irritation. [5]

Time points observed in studies (not a schedule for your skin):

Who should be careful?

If you have darker skin, sensitive skin or skin that marks easily, start acids more cautiously. Among 473 superficial clinic peels in Fitzpatrick skin types III to VI, 3.8% led to complications, most often crusting, post-inflammatory hyperpigmentation and redness. The darkest skin type (VI) had clearly higher odds of side effects. [15]

According to a review of peel complications, they are more likely in darker skin types, with certain peeling agents and with sun exposure after treatment; the first step in prevention is identifying who is at risk. [3] If you already have stinging, dryness and flaking, focus on your skin barrier first. A review of salicylic acid peels also covers salicylism (poisoning from salicylic acid building up in the body); ask a clinician before applying a high-strength product to a large area. [2]

With rosacea, eczema or active, inflamed acne, talk to your clinician before adding a new acid.

Professional chemical peels: a procedure for a clinician

A professional chemical peel is a medical procedure in which the acid type, concentration, frequency and pressure of application are chosen for the target depth. Medium-depth peels use TCA, and deep peels use high-strength TCA or phenol. According to an expert review, success depends on the physician understanding the chemistry, biology, indications and side effects. [9]

Both results and complications increase with depth. [10] For mild to moderate acne, common clinic peels appear similarly effective and well tolerated, but study quality is too low to call any one peel better. [6] We give no procedure steps here; that is a dermatologist’s call.

Frequently asked questions

Should you choose AHA or BHA for breakouts?

Not necessarily one over the other; in clinic peels for acne, the two performed similarly. A systematic review found no difference between glycolic and salicylic acid peels, though study quality was low. [6] In a small split-face trial, the salicylic acid peel’s effect lasted two months after treatment and it caused fewer early side effects. [12]

How long does a chemical peel take to work?

There is no single timeline; it depends on the strength and type of treatment. In a clinic acne study with 30% peels, a significant effect appeared from the second session. [12] The home trial with 8% AHA creams assessed results at week 22, and the benefit was modest. [5]

What should you do after a chemical peel?

Protect your skin from the sun above all; sun exposure after a peel makes complications more likely. [3] After a professional peel, follow your clinician’s aftercare instructions. As general advice, do not pick at peeling skin or add other exfoliants in the same days.

Can you use AHA or BHA while pregnant?

Our sources contain no study that answers this, so decide with your clinician. None of the studies here assessed safety in pregnancy, so we call neither at-home AHA and BHA products nor professional peels safe or unsafe in pregnancy.

References

1. Tang SC, Yang JH. Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules. 2018;23(4). PubMed · DOI
2. Arif T. Salicylic acid as a peeling agent: a comprehensive review. Clin Cosmet Investig Dermatol. 2015;8:455-461. PubMed · DOI
3. Costa IMC, Damasceno PS, Costa MC, Gomes KGP. Review in peeling complications. J Cosmet Dermatol. 2017;16(3):319-326. PubMed · DOI
4. Kaidbey K, Sutherland B, Bennett P, et al. Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatol Photoimmunol Photomed. 2003;19(1):21-27. PubMed · DOI
5. Stiller MJ, Bartolone J, Stern R, et al. Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-controlled clinical trial. Arch Dermatol. 1996;132(6):631-636. PubMed
6. Chen X, Wang S, Yang M, Li L. Chemical peels for acne vulgaris: a systematic review of randomised controlled trials. BMJ Open. 2018;8(4):e019607. PubMed · DOI
7. Tan MG, Kim WB, Jo CE, Nabieva K, Kirshen C, Ortiz AE. Topical treatment for postinflammatory hyperpigmentation: a systematic review. J Dermatolog Treat. 2022;33(5):2518-2526. PubMed · DOI
8. Krstonošić V, Ćirin D. Are cosmetics based on alpha hydroxy acids safe to use when purchased over the internet? Toxicol Ind Health. 2022;38(12):835-838. PubMed · DOI
9. Fischer TC, Perosino E, Poli F, Viera MS, Dreno B, Cosmetic Dermatology European Expert Group. Chemical peels in aesthetic dermatology: an update 2009. J Eur Acad Dermatol Venereol. 2010;24(3):281-292. PubMed · DOI
10. Lee KC, Wambier CG, Soon SL, et al. Basic chemical peeling: Superficial and medium-depth peels. J Am Acad Dermatol. 2019;81(2):313-324. PubMed · DOI
11. Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol. 2010;3:135-142. PubMed · DOI
12. Kessler E, Flanagan K, Chia C, Rogers C, Glaser DA. Comparison of alpha- and beta-hydroxy acid chemical peels in the treatment of mild to moderately severe facial acne vulgaris. Dermatol Surg. 2008;34(1):45-50; discussion 51. PubMed · DOI
13. Smith WP. Epidermal and dermal effects of topical lactic acid. J Am Acad Dermatol. 1996;35(3 Pt 1):388-391. PubMed · DOI
14. Liu H, Yu H, Xia J, et al. Topical azelaic acid, salicylic acid, nicotinamide, sulphur, zinc and fruit acid (alpha-hydroxy acid) for acne. Cochrane Database Syst Rev. 2020;5(5):CD011368. PubMed · DOI
15. Vemula S, Maymone MBC, Secemsky EA, et al. Assessing the safety of superficial chemical peels in darker skin: A retrospective study. J Am Acad Dermatol. 2018;79(3):508-513.e2. PubMed · DOI