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AHAs, BHAs and PHAs are chemical exfoliants. AHAs work on the skin surface, BHAs are oil-soluble and used for pore-prone skin, and PHAs are larger molecules often described as gentler. Many Korean toners blend all three. Start a few times a week, and use sunscreen daily.
Exfoliating acids can sound intimidating, yet they are common in Korean routines. At Daebak, a Seoul-based Korean culture and product company, this is a frequent question, so here is a beginner-friendly explanation. It is general information, not medical advice.
AHA, BHA and PHA at a glance
| AHA | BHA | PHA | |
|---|---|---|---|
| Full name | Alpha hydroxy acid | Beta hydroxy acid | Polyhydroxy acid |
| Common example | Glycolic or lactic acid | Salicylic acid | Gluconolactone |
| Usually described as | Surface exfoliation, smoother-looking texture | Oil-soluble, used for pore-prone skin | Larger molecule, often called gentler |
The US Food and Drug Administration says the most common AHAs in cosmetics are glycolic acid and lactic acid, and that AHA products work by exfoliation, removing the outer layer of skin. For BHAs, the FDA says salicylic acid is the one most commonly used in cosmetics, and notes that from a chemist's perspective it is not a true BHA, although cosmetic companies often call it one. It also records the claim, which it attributes to marketing rather than confirming, that BHAs can improve texture with less of the occasional irritation linked to AHAs.
Why Korean brands blend all three
Instead of choosing one, many Korean formulas combine low levels of AHA, BHA and PHA with soothing ingredients. The SOME BY MI AHA BHA PHA 30 Days Miracle Toner is one example in a toner format. SOME BY MI also makes a serum and a cleansing foam in the same line, so you can see how one idea is applied across steps.
SOME BY MI AHA BHA PHA 30 Days Miracle Toner. See details.
How to use an exfoliating toner
- Patch test a small area first.
- Start slowly. A few times a week is a common starting point; follow the pack.
- Apply after cleansing with a cotton pad or clean hands.
- Follow with moisturizer to keep skin comfortable.
- Use sunscreen every morning. Exfoliating acids are normally used alongside daily sun protection.
- Do not stack strong actives such as retinol on the same night until you know how your skin reacts.
Why sunscreen matters with acids
The FDA cites studies in which applying AHAs increased skin sensitivity to UV: after four weeks, volunteers' UV-induced reddening was 18 percent higher and UV-induced cell damage roughly doubled on average. The FDA says the effect was reversible and had gone within a week of stopping. It advises sun protection while using AHA products and for a week afterward. For BHAs, the FDA's page cites the Cosmetic Ingredient Review panel, which concluded that salicylic acid ingredients are safe as used when formulated to avoid irritation and increased sun sensitivity, and that directions should include daily sun protection where sun sensitivity would be expected.
Who should be careful
Very sensitive, broken or recently irritated skin often needs a break from acids. If you are pregnant or nursing, or are using prescription skincare, ask your doctor or dermatologist before adding exfoliating acids.
Starting a routine
If you are putting a routine together from scratch, the Daebak K-Beauty Box is a seasonal box of Korean skincare and makeup curated in Seoul. Contents change by season, so specific products are not guaranteed.
FAQ
What is the difference between AHA and BHA?
AHAs are water-soluble and work on the skin surface. BHAs are oil-soluble and are commonly used for pore-prone skin.
Is PHA gentler than AHA?
PHAs have larger molecules and are often described as gentler, though everyone's skin is different.
How often should I use an AHA BHA PHA toner?
Many people start a few times a week and adjust. Follow the product instructions.
Can I use it with retinol?
Many people separate them onto different nights. If unsure, ask a dermatologist.
