Ahas, bhas & phas: exfoliating acids for smoother, clearer-looking skin

How it works

AHAs are water-soluble molecules that work at the surface of skin by lowering the pH at the stratum corneum, which weakens the protein-lipid bonds between dead cells (desmosomes) and accelerates their natural shedding (desquamation)1, ¹². Because AHAs work on a pH-dependent basis, formulation pH matters — lower pH equals more active acid, but also more potential irritation. Glycolic acid is the smallest AHA molecule, which means it penetrates fastest and exfoliates most aggressively at the same pH and concentration as larger AHAs¹,5. Lactic acid is larger and gentler, and additionally acts as a humectant — bringing some hydration along with exfoliation¹¹. Mandelic acid is the largest, with the slowest, gentlest action — well suited for sensitive-feeling skin and skin tones prone to post-inflammatory hyperpigmentation⁶.

BHAs — primarily salicylic acid — are oil-soluble. This lets them penetrate the lipid-rich environment inside pores, where they stimulate natural exfoliation and help clear keratin and sebum debris that contribute to congestion ¹⁰. For the same reason, salicylic acid is the BHA of choice for breakout-prone skin⁷.

PHAs like gluconolactone work by the same desmosome-weakening mechanism but with much larger molecules — meaning gentler, slower, and more tolerated exfoliation, particularly for sensitivity-prone skin1.

The visible result of consistent use across all three families: smoother-looking texture, more even-looking tone, fewer visible blemishes, and a more refined-looking complexion² ⁵. For a deeper professional overview, see The International Dermal Institute's Acid Families Decoded: AHA, BHA, PHA and How They Behave and Why pH Matters in Skin and Skin Care.

Skin types & concerns it suits

• Breakout-prone and oily skin: salicylic acid (BHA) penetrates pore lining lipids to clear keratin plugs and excess sebum10
• Dull, uneven-looking skin: glycolic and lactic acid (AHA) accelerate desquamation for a brighter-looking complexion1
• Sensitive-feeling skin: mandelic acid, lactic acid, or PHAs deliver exfoliation with less stinging risk than glycolic1
• Dry skin: lactic acid offers humectant benefits alongside exfoliation
• Mature skin: AHA-rich regimens help reveal smoother-looking skin with reduced appearance of fine lines⁹
• Hyperpigmentation-prone skin tones: mandelic acid and PHAs reduce the post-inflammatory pigmentation risk associated with stronger AHAs

How AHAs, BHAs, PHAs and enzymes compare

The four families behave differently — the right choice depends on skin type and concern. AHAs dissolve the lipid "cement" between cells via low pH⁸; BHAs penetrate oil-filled pores to clear congestion⁷; PHAs work like AHAs but with larger, gentler molecules1; and enzymes (papain, bromelain, pumpkin) digest the protein bonds between cells at near-neutral pH — the gentlest option for sensitivity-prone skin. AHAs and BHAs require acidic pH to remain active; enzymes do not, which makes enzyme exfoliants (such as papain combined with salicylic acid) a strong fit for daily-use routines on most skin types. For more on choosing the right exfoliant, see The International Dermal Institute's Ingredients 101: Exfoliation — Choosing the Right Acid or Enzyme for Every Skin Type. For a professional view of in-treatment chemical peels (and how they relate to at-home AHA/BHA use), see Professional's Guide to Chemical Peels.

Tips for use

• Introduce acid-based exfoliants gradually — start 2–3 times per week and build up as tolerated
• Always wear broad-spectrum SPF 30 or higher when using AHAs/BHAs — chemical exfoliation can transiently increase UV sensitivity
• Avoid pairing strong AHAs with retinol on the same night until your skin is fully acclimated to both ingredients
• For breakout-prone skin, look for salicylic acid in cleansers and toners (where the contact time and rinse-off support consistent daily use)
• For sensitive-feeling skin, start with a lactic acid or PHA serum before progressing to glycolic⁸ ¹¹

Safety & considerations

• Sun sensitivity: AHAs and BHAs can transiently increase UV reactivity — daily SPF is non-negotiable
• Pregnancy and breastfeeding: always consult your healthcare provider before introducing any new active during pregnancy or breastfeeding; high-concentration salicylic acid peels and products containing both salicylic acid and retinoids should be avoided
• Layering caution: don't combine high-strength AHAs/BHAs with retinol or benzoyl peroxide in the same routine until your skin is acclimated. Alternate evenings or use them at different times of day
• Tingling vs. burning: mild tingling on application is normal; persistent burning, redness, or peeling is a sign to scale back frequency

The AHA/BHA family is wide and varied, with each acid suiting different skin types and concerns. Salicylic acid, the workhorse beta hydroxy acid, is widely used in cleansers, serums, boosters, washes, and post-breakout treatments. Salicylic acid is oil-soluble, so it can penetrate into pores where it stimulates natural exfoliation and helps clear impacted follicles to minimize the appearance of breakouts¹⁰. Lactic acid — gentler and more hydrating — features in eye serums, brightening serums, and body creams. As an alpha hydroxy acid, lactic acid helps remove dull surface cells, smooth and retexturize skin, and reveal smoother-looking skin with the appearance of reduced fine lines and wrinkles¹¹. Glycolic acid, the smallest AHA molecule, is a staple of glycolic cleansers, where it exfoliates by speeding up the rate at which dead skin cells slough off, revealing newer, brighter, healthier-looking skin¹,5.

Other acids round out the family. Phytic acid in cleansing formulas helps brighten the appearance of skin¹³. Lactic acid paired with malic acid — alpha hydroxy acids that work at the surface of skin to lift away dull cells and reveal a smoother-looking complexion1. When lactic acid and salicylic acid are combined, the result is alpha and beta hydroxy action together, stimulating exfoliation of cells for a smoother skin surface and supporting the look of refreshed, refined skin. A 12% AHA/PHA blend of mandelic, glycolic, and phytic acids provides intensive exfoliation for visibly brighter, more even-toned skin.

For first-time users navigating the acid family, we recommend speaking with a skin therapist via Face Mapping skin analysis to choose the right acid (or enzyme) for your skin type. For perspective on consistent regimens vs. cycling, see The International Dermal Institute's Consistent Routines vs. Skincare Cycling.

FAQs

Q: What's the difference between AHAs and BHAs?
A: AHAs (glycolic, lactic, mandelic, malic acid) are water-soluble and work at skin's surface to lift away dull cells and smooth texture⁸. BHAs (salicylic acid) are oil-soluble, so they can penetrate into pores to help clear congestion⁷. AHAs are typically chosen for tone and texture concerns; BHAs for breakout-prone and oily skin.

Q: What about PHAs — how are they different?
A: PHAs (poly hydroxy acids like gluconolactone) work by the same desmosome-weakening mechanism as AHAs but use much larger molecules, which makes them slower and gentler⁸. They're well suited for sensitive-feeling skin and tend to be lower-irritation than glycolic acid.

Q: What skin concerns do exfoliating acids help address?
A: They help smooth the appearance of texture, brighten the look of dullness, reduce the appearance of fine lines and pores, and minimize the appearance of breakouts and congestion¹ ² ⁷ ⁹.

Q: Which acid is best for breakout-prone skin?
A: Salicylic acid (a BHA) is the standard choice. Because it's oil-soluble, it penetrates pore lipids to stimulate natural exfoliation and clear impacted follicles⁷ ¹⁰.

Q: Is lactic acid a good option for sensitive-feeling skin?
A: Lactic acid is one of the gentler AHAs and also acts as a humectant. It helps remove dull surface cells and reveal smoother-looking skin with the appearance of reduced fine lines¹¹.

Q: How is glycolic acid different from other AHAs?
A: Glycolic acid is the smallest AHA molecule, which means it penetrates fastest and exfoliates most efficiently at a given pH and concentration — revealing newer, brighter-looking skin more rapidly¹,5. The trade-off is more potential for irritation than larger AHAs.

Q: How often should I use exfoliating acids?
A: Start with 2–3 times per week and gradually increase as your skin builds tolerance. Some daily-use formulas (such as gentle glycolic cleansers, where contact time is short) are appropriate for daily use. Consistency over time delivers the best visible results.

Q: Do I need SPF when using AHAs or BHAs?
A: Yes. Exfoliating acids can transiently increase sun sensitivity, so pairing them with broad-spectrum SPF every morning is essential to protect your skin and support visible results.

Q: Can I use exfoliating acids with retinol?
A: Possible, but proceed with care. Don't combine high-strength acids with retinol on the same night until your skin is fully acclimated to both. Alternate evenings is a safer entry point. Some buffered formulas pair retinol with salicylic acid specifically so the two can be used together.

Q: Are AHAs and BHAs safe during pregnancy?
A: Always consult your healthcare provider before introducing any new active during pregnancy or breastfeeding; high-concentration salicylic acid peels are typically avoided.

Q: What's the difference between acid exfoliants and enzyme exfoliants?
A: Acids work by dissolving the lipid bonds between cells (low pH dependent); enzymes like papain digest the protein bonds between cells (near-neutral pH). For sensitivity-prone skin, enzymes are generally gentler. For breakout-prone skin, salicylic acid's pore-penetrating action is hard to match with enzymes alone.

Further reading from The International Dermal Institute

• Acid Families Decoded: AHA, BHA, PHA and How They Behave
• Why pH Matters in Skin and Skin Care
• Ingredients 101: Exfoliation — Choosing the Right Acid or Enzyme for Every Skin Type
• The Rising Tide of Adult Breakouts: Understanding and Addressing the New Normal
• Ingredients 101: Brightening Agents — What Actually Works and How to Spot Them
• Consistent Routines vs. Skincare Cycling: What the Skin Responds To
• Professional's Guide to Chemical Peels
• Case Clinic: "My Skin Hates Everything After a Few Weeks"

References

1. Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clinical, Cosmetic and Investigational Dermatology. 2010;3:135-142. 2. Evaluating the Efficacy and Safety of Alpha-Hydroxy Acids in Dermatological Practice: A Comprehensive Clinical and Legal Review. Clinical, Cosmetic and Investigational Dermatology. 2024;17:1613-1632. 3. Castillo DE, Keri JE. A Comprehensive Bibliographic Review Concerning the Efficacy of Organic Acids for Chemical Peels Treating Acne Vulgaris. Dermatology and Therapy. 2023;13(11):2573-2593. 4. Moghimipour E. Hydroxy Acids, the Most Widely Used Anti-aging Agents. Jundishapur Journal of Natural Pharmaceutical Products. 2012;7(1):9-10. 5. Tang SC, Yang JH. Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules. 2018;23(4):863. 6. Jacobs SW, Culbertson EJ. Effects of Topical Mandelic Acid Treatment on Facial Skin Viscoelasticity. Facial Plastic Surgery. 2018;34(6):651-656. 7. Gao Y, Li X, Zhang L, et al. Clinical efficacy of a salicylic acid–containing gel on acne management and skin barrier function. Journal of Cosmetic Dermatology. 2025;24(6):e16728. 8. Feng X, Shang J, Gu Z, et al. Lactic Acid Chemical Peeling in Skin Disorders. Clinical, Cosmetic and Investigational Dermatology. 2024;17:1029-1038. 9. Bogdan C, Iurian SM, Tomuta I, et al. An antiaging skin care system containing alpha hydroxy acids and vitamins improves the biomechanical parameters of facial skin. Clinical, Cosmetic and Investigational Dermatology. 2014;7:329-336. 10. Arif T. Salicylic acid as a peeling agent: a comprehensive review. Clinical, Cosmetic and Investigational Dermatology. 2015;8:455-461. 11. Stiller MJ, Bartolone J, Stern R, et al. Epidermal and dermal effects of topical lactic acid. Journal of the American Academy of Dermatology. 1996;34(4):688. 12. Atzori L, Brundu MA, Orru A, Biggio P. Clinical evaluation of glycolic acid chemical peeling in patients with acne vulgaris: a randomized, double-blind, placebo-controlled, split-face comparative study. Dermatologic Surgery. 2014;40(3):314-320. 13. Houshmand EB, Moy RL. Effect of glycolic acid, phytic acid, soothing complex-containing emulsion on hyperpigmentation and skin luminosity: a clinical evaluation. Journal of Cosmetic Dermatology. 2021;20(7):2168-2173. 14. Sarkar R, Garg V, Bansal S, et al. Comparative Study of 35% Glycolic Acid, 20% Salicylic–10% Mandelic Acid, and Phytic Acid Combination Peels in the Treatment of Active Acne and Postacne Pigmentation. Journal of Cutaneous and Aesthetic Surgery. 2019;12(3):158-163.