What is the difference between AHA, BHA, and PHA?

All three are chemical exfoliants that dissolve dead skin cells, but they work at different depths. AHAs (alpha hydroxy acids like glycolic and lactic) are water-soluble and work on the surface — best for dullness, dark spots, and fine lines. BHAs (beta hydroxy acids, primarily salicylic) are oil-soluble and penetrate into pores — best for blackheads, acne, and oily skin. PHAs (polyhydroxy acids like gluconolactone) are larger molecules that work more slowly and gently — best for sensitive skin, compromised barriers, or first-time acid users.

Can I use AHA and BHA together?

Yes, but not in the same application. Use one in the morning and one at night, or alternate nights. Both acids lower skin pH and accelerate cell turnover — stacking them at the same time increases irritation risk. On melanin-rich skin specifically, stacked acids are a leading cause of post-inflammatory hyperpigmentation, so cycle them rather than layer.

Which acid is best for sensitive skin?

PHAs (gluconolactone, lactobionic acid) are the gentlest. Their larger molecule size means slower penetration and less irritation. Mandelic acid is also a great choice — it's technically an AHA but its larger molecule makes it the gentlest AHA. For very sensitive or barrier-compromised skin, start with PHA 4 to 8 percent twice weekly and build from there.

How often should I use chemical exfoliants?

Start at 2 to 3 times per week. Build up to daily only after 4 to 6 weeks of tolerance. On melanin-rich skin or sensitive skin, many people do best at 3 to 4 times per week long-term — daily use isn't necessary for results and increases PIH risk.

AHA vs BHA vs PHA: Which Acid Is Right for You (2026 Guide)

Three families of chemical exfoliants. Different molecule sizes. Different effects on skin. Most "chemical exfoliation" advice treats them as interchangeable — they aren't. Here's how to pick the right one for your skin type, your concern, and your tolerance.

Chemical exfoliation gets reduced to a simple choice in most skincare content: "use an acid." Reality is more nuanced. The acid family you pick — and the specific molecule within it — changes everything about your skin's response. This matters more on melanin-rich skin (Fitzpatrick V–VI), where the wrong acid family at the wrong concentration is the leading cause of post-inflammatory hyperpigmentation in adult skincare routines.

The 3 acid families at a glance

Family	Best for	Irritation
AHA (Glycolic, Lactic, Mandelic)	Dullness, dark spots, fine lines, surface texture	Moderate
BHA (Salicylic)	Acne, blackheads, oily skin, clogged pores	Moderate
PHA (Gluconolactone, Lactobionic)	Sensitive skin, barrier repair, first-time acid users	Very low

AHAs — for surface concerns

Water-soluble. Work on the very top layer of skin. Dissolve the bonds holding dead cells together so they shed naturally.

Glycolic acid — smallest AHA molecule. Most potent. Best for fine lines, dullness, and texture. Irritation risk is real.
Lactic acid — larger than glycolic. Adds hydration. Good middle option.
Mandelic acid — largest AHA molecule. Gentlest. Best for sensitive skin and Fitzpatrick V–VI. Mandelic acid guide.
Malic, tartaric, citric — minor AHAs, usually formulation supports rather than primary actives.

BHAs — for pores and acne

Oil-soluble. The only acid family that can penetrate INTO pores and dissolve the sebum + dead-skin plugs that cause blackheads and acne.

Salicylic acid — the BHA you'll see most. 0.5–2% is the OTC range. Anti-inflammatory in addition to exfoliating. Best for acne-prone skin, blackheads, oily T-zones.
Betaine salicylate — gentler salicylic alternative used in Korean skincare. Less drying.

PHAs — for sensitive skin

Newer category. Larger molecules than AHAs. Penetrate much more slowly = less irritation, less photosensitivity, gentler exfoliation. Also have humectant properties (they pull water into skin).

Gluconolactone — the most common PHA. Effective at 4–10%.
Lactobionic acid — slightly stronger PHA with antioxidant activity.
Galactose — newest PHA, antioxidant-focused.

The melanin-rich skin pick For Fitzpatrick V–VI, start with PHA or mandelic acid. The larger molecule sizes mean slower penetration and less PIH risk. Glycolic acid at 10%+ on darker skin frequently produces post-exfoliation dark spots that take months to fade — defeating the purpose. PHA first, mandelic second, lactic third. Glycolic last if at all.

Concentration guide

AHA: 5–10% for daily use. 20–30% for at-home peels (weekly maximum).
BHA: 0.5–2%. Higher concentrations don't perform better — they just irritate.
PHA: 4–10%. PHA tolerates higher concentrations because of slow penetration.

The cardinal rules

One acid family at a time when starting. Don't layer AHA + BHA + PHA in one routine.
Daily SPF is non-negotiable on any acid. UV exposure on freshly exfoliated skin = more PIH.
Pause acids before any waxing, dermal-needling, or laser treatment. Resume 1 week after.
Don't combine acids with retinol on the same evening. Alternate nights.

Find out which acid family fits YOUR skin specifically

Lumière scans your skin and tells you whether PHA, mandelic, lactic, glycolic, or salicylic is the right starting point for your barrier state. Free first scan.

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AHA vs BHA vs PHA: Which Acid Is Right for You