AHA, BHA and PHA are three families of chemical exfoliants: AHAs are water-soluble and work at the surface, BHAs are oil-soluble and get inside the pore, PHAs have larger molecules and penetrate more slowly, which generally makes them the best tolerated.
The three families
AHA — alpha hydroxy acids
The best known are glycolic acid and lactic acid. They are water-soluble, so they work on the surface layer. You'll find them in products aimed at texture and evenness of tone.
BHA — beta hydroxy acids
The BHA is salicylic acid. Being oil-soluble, it can get into the sebum that fills a pore, which is why it appears so often in products for oily skin or visible pores.
PHA — polyhydroxy acids
Gluconolactone and lactobionic acid are the common ones. They have larger molecules, penetrate more slowly, and are usually the starting point for sensitive skin or for anyone who has never used acids.
Which to choose
- Oily skin, visible pores, breakouts → BHA
- Dull skin, uneven texture → AHA
- Sensitive skin, or a first time → PHA
Many Korean products combine all three: that is the case with Some By Mi's Miracle 30 Days AHA-BHA-PHA line, available as serum (€20.90), cream (€19.90) and cleansing foam (€15.90). Esfolio's 3HA Clear line works on the same idea and starts at €8.90.
Among the single-acid products: Green Plum Refreshing AHA + BHA by Beauty of Joseon (€15.90) and the two peeling gels in scrubs and peels.
How to start, without damage
This matters more than which product you pick.
- One at a time. One new product with acids, not two at once.
- Twice a week to begin with, in the evening. Increase only if your skin responds well — and not everyone gets to daily use, nor needs to.
- Sunscreen every day. Chemical exfoliants make skin more sensitive to sunlight. Without daily SPF, the net result can be worse than where you started.
- Don't layer them with retinol in the same application unless your skin is already used to both. Alternating evenings is the safer approach.
Signs you're overdoing it
Skin that feels tight, that stings slightly with products it used to tolerate, persistent redness, or a strange "taut" shine. These are the classic signs of a skin barrier under stress: the answer is to remove, not to add.
In that case stop the acids for a week or two and go back to a minimal routine — gentle cleanser, something soothing, centella if you have it, cream, sunscreen — until your skin recovers.
What about scrubs?
Grain-based scrubs do a different and blunter job. Korean routines generally favour chemical exfoliation because it is easier to control: the concentration and frequency are written on the packet, the force you scrub with isn't.
Either way, exfoliation is a weekly step, not a daily one. Where it sits in the sequence is in what order to apply skincare in.