AHA vs BHA vs PHA: How Korean Exfoliating Acids Differ

I own an AHA toner, a BHA toner and a PHA toner. At one point I owned two of each, because the second set had prettier packaging and the word “gentle” in a nicer font. Same acids, same approximate concentrations, twice the shelf space and a lingering suspicion that I was exfoliating my wallet.

The three families are often presented as a simple spectrum from strong to gentle, but the real differences are about chemistry, not just strength. Each family works differently, suits different skin concerns and carries different caveats about sun sensitivity. And a startling number of “rival” acid toners share a contract manufacturer, a base formula and a loading dock: they part ways at the label printer.

The three families at a glance

Property	AHA	BHA	PHA
Full name	Alpha hydroxy acid	Beta hydroxy acid	Polyhydroxy acid
Common examples	Glycolic acid, lactic acid, mandelic acid	Salicylic acid	Gluconolactone, lactobionic acid
Solubility	Water-soluble	Oil-soluble	Water-soluble
Where it works	Skin surface	Skin surface and inside pores	Skin surface
Molecule size	Small (glycolic) to medium (mandelic)	Small	Large
Typical sensation	Tingling or stinging at higher concentrations	Mild tingling	Minimal

AHAs: surface exfoliation

Alpha hydroxy acids dissolve the bonds between dead cells on the skin surface. The most common in K-beauty are glycolic acid (the smallest, fastest-acting) and lactic acid (slightly larger, often gentler). Mandelic acid, larger still, appears in products aimed at sensitive or acne-prone skin. The size difference matters more than the marketing lets on. Glycolic acid has the smallest molecular weight of the group, which means it penetrates most readily and also causes the most irritation at comparable concentrations. Lactic acid is a step up in size and tends to act as a mild humectant alongside its exfoliating work. Mandelic acid is larger again and slower to penetrate, which is why it turns up in formulas marketed toward reactive or darker skin tones where post-inflammatory hyperpigmentation is a concern [2].

The key clinical concern with AHAs is sun sensitivity. FDA-sponsored studies found that four weeks of applying a 10% glycolic acid cream increased UV-induced reddening by 18% and roughly doubled UV-induced cell damage, with wide variation between individuals. The effect reversed within a week of stopping [1]. This applies to all AHAs, not just glycolic acid. The mechanism involves thinning the outer layer of dead cells that normally provide some passive UV buffering. Fewer dead cells means less of a shield, which is a real trade-off: smoother texture, less built-in protection [2].

The Cosmetic Ingredient Review panel considers AHA products safe at 10% concentration or below with a pH of 3.5 or higher, provided they are formulated or labeled to encourage sun protection [1]. Most K-beauty AHA toners fall within these parameters, though the pH is rarely printed on the outer packaging. In the EU, the cosmetics regulation requires specific labeling when products contain AHAs above certain thresholds, and Annex III restricts several ingredients including salicylic acid to set concentrations in leave-on and rinse-off products [5]. Korean functional cosmetic rules, meanwhile, govern claims about wrinkle improvement and whitening but do not separately regulate AHA concentration in the same way. So the same acid, in the same concentration, may come with different warnings depending on which market the bottle was packed for.

BHA: into the pores

Salicylic acid is the main BHA used in skincare. Its oil-solubility allows it to penetrate into pores, making it suited for oily and acne-prone skin. A review of salicylic acid as a peeling agent describes its keratolytic (cell-loosening), comedolytic (pore-clearing) and anti-inflammatory properties [4]. That anti-inflammatory side is often overlooked in K-beauty marketing, which tends to focus on the pore-clearing angle. In clinical use, salicylic acid’s anti-inflammatory action is part of why it appears in so many acne treatment guidelines: it is not just dissolving the plug, it is calming the area around it [4].

In K-beauty, salicylic acid commonly appears at 0.5–2% in toners and spot treatments. The EU restricts salicylic acid as a preservative and as an active ingredient in cosmetics, with concentration limits that depend on whether the product is rinse-off or leave-on [5]. Korea allows it under its own limits, and the US treats products containing salicylic acid for acne as over-the-counter drugs, which adds labeling requirements that a Korean export product sold as a cosmetic may not carry. Same ingredient, different rules, different boxes. Read the version in your hand.

BHA tends to be gentler than AHAs at comparable levels of exfoliation, partly because it self-limits: once it dissolves the oil in a pore, it stops penetrating deeper. Less data exists specifically on BHA and UV sensitivity compared with AHAs. The FDA’s published summary focuses on AHAs. The AAD still recommends sunscreen with any chemical exfoliant [6].

PHAs: the gentlest option

Polyhydroxy acids are structurally similar to AHAs but with larger molecules. That larger size means they penetrate more slowly and tend to cause less irritation. A review of PHAs describes them as providing exfoliation plus humectant properties (they attract water), making them a dual-function ingredient [3].

Gluconolactone and lactobionic acid are the two PHAs you will encounter most often in K-beauty. They suit sensitive skin, rosacea-prone skin and skin that cannot tolerate glycolic or lactic acid. The trade-off: fewer head-to-head studies compare their effectiveness with AHAs, so “as effective but gentler” is a reasonable hope rather than a proven conclusion.

How pH and concentration interact

An acid’s effectiveness depends on both its concentration and the product’s pH. A 10% glycolic acid product at pH 3.5 exfoliates very differently from one at pH 4.5. Most consumer products do not print the pH on the label, so you cannot always judge strength from the percentage alone.

K-beauty exfoliating toners and pads often combine a lower acid concentration with soothing ingredients like centella, panthenol or allantoin. This can make them more tolerable than a Western product with a higher concentration and fewer buffers, but it also means the exfoliating effect may be milder.

The trend cycle and the factory floor

Here is the part nobody films. Acid toners are one of the easiest categories for a contract manufacturer to produce at scale. Water, an acid at a set percentage, a pH buffer, a handful of soothing botanicals, a humectant, a preservative system and a fragrance decision. Two brands can brief the same factory with the same target pH and the same headline acid, receive essentially the same base formula, and launch in the same month with different fonts and different claims about “innovation”. One says “gentle daily resurfacing.” The other says “intensive renewal.” The list says the same thing.

The mascot rotation applies here too. A few years ago the K-beauty acid aisle was built around glycolic acid. Then lactic acid had a turn, partly because it sounded gentler. Then PHA arrived as the “next generation” option. The molecules did not change. The campaigns changed. The acids are still glycolic, lactic and salicylic doing their respective jobs, with PHA as the quieter newcomer. The ingredient list is the only part of the bottle that is under oath; the adjective on the front is not.

Choosing between them

Skin concern	Consider first	Why
Dull, rough texture	AHA (glycolic or lactic acid)	Surface exfoliation improves texture
Oily skin, blackheads, acne	BHA (salicylic acid)	Oil-soluble, works inside pores
Sensitive or rosacea-prone skin	PHA (gluconolactone)	Larger molecule, gentler, humectant
Dry skin with flakiness	AHA (lactic acid)	Gentler AHA with some humectant properties

The fair summary: AHAs exfoliate the surface and increase sun sensitivity; BHA gets into pores; PHAs are gentler with less data behind them. Pick by skin concern, not by which one had the better campaign this quarter.

You can use more than one acid type, but not necessarily at the same time. The AAD advises starting slowly and not combining exfoliants unless your skin has adjusted to each one individually [6].

Now look at your shelf. If you have an AHA toner and a PHA toner and a BHA spot treatment and a mixed-acid pad, that is not a curated routine. That is a collection. Three acids doing three jobs is a plan; three products per acid is a fan club with a budget problem.

What to check on the label

1. Which acid. The INCI name tells you the specific acid, not just the family.
2. Where it appears on the ingredient list. Higher means more by weight above the 1% threshold.
3. Directions on frequency. If a product says two to three times per week, respect that.
4. Soothing ingredients. Centella, panthenol and allantoin suggest the formula is designed to offset irritation.
5. Fragrance and essential oils. Adding potential irritants to an already active product increases the risk of a reaction.

For where exfoliating products fit alongside your other layers, see where toner, essence and serum overlap. An exfoliating toner is not a hydrating toner: do not layer it the same way.

Pick one acid. Use it long enough to learn what it does. Buy the second only when the first has earned a refill.

When to see a clinician first. Stop using an exfoliating acid if your skin stays red, peels excessively or stings persistently. See a dermatologist before using chemical exfoliants if you have rosacea, eczema, active acne on prescription treatment or recently had a cosmetic procedure. Always use sunscreen while using any exfoliating acid. Seek urgent care for swelling of the face, lips or eyes.