PHA vs AHA vs BHA: A Beginner’s Guide to Chemical Exfoliants
Chemical exfoliants are one of the areas where Korean and Western skincare philosophies diverge most visibly. Western routines often favor stronger, faster-acting acids used a few times a week at higher concentrations. Korean routines tend to favor gentler, more frequent use of milder formulations — which is exactly why understanding the difference between PHA, AHA, and BHA matters more than just memorizing three acronyms. Here’s a full breakdown, with a focus on how Korean brands actually formulate and market these acids differently.
The Basics: What Each Acronym Means
- AHA (Alpha Hydroxy Acid) — water-soluble acids that exfoliate the skin’s surface. Common types include glycolic acid (smallest molecule, deepest penetration) and lactic acid (larger molecule, gentler, with added hydrating properties).
- BHA (Beta Hydroxy Acid) — oil-soluble, meaning it can penetrate into pores and dissolve built-up sebum and debris. Salicylic acid is essentially the only BHA used in skincare.
- PHA (Polyhydroxy Acid) — the newest and gentlest category, with larger molecules than AHAs that exfoliate more slowly and superficially, while also offering humectant (moisture-binding) properties. Common types include gluconolactone and lactobionic acid.
How Korean Brands Approach Exfoliation Differently
Korean skincare culture has a specific, widely used term for physical exfoliation and its risks: “각질” (gakjil, or dead skin cells) removal is treated as something to manage gently and gradually rather than aggressively scrub away. This philosophy carries over directly into chemical exfoliant formulation. Where a Western drugstore AHA/BHA product might sit at 8-10% concentration for weekly use, a comparable Korean product — for example, from COSRX’s famous BHA Blackhead Power Liquid — is formulated at around 0.5% salicylic acid explicitly so it can be used more frequently without over-stripping the skin.
This is a genuinely important cultural and formulation difference to understand: if you’re used to Western-strength acids and switch to a Korean BHA toner expecting the same intensity, you may find it “too gentle” — but that’s by design, not a weakness. Korean formulators generally prioritize long-term barrier health over dramatic, fast results.
AHA: Best For Surface Texture and Dullness
AHAs work by dissolving the “glue” (desmosomes) that holds dead skin cells together on the surface of the skin, revealing smoother, brighter skin underneath. They’re best suited for:
- Dull, uneven texture
- Mild hyperpigmentation and post-acne marks
- Fine lines and early signs of sun damage (glycolic acid in particular has anti-aging research behind it)
Popular Korean AHA products: Some By Mi AHA-BHA-PHA 30 Days Miracle Toner (a well-known “gateway” acid toner for beginners, deliberately low-strength), Pyunkang Yul Peeling Gel, Isntree Hyaluronic Acid Toning Gel Pad (contains gentle glycolic and lactic acid).
BHA: Best For Pores, Oil, and Blackheads
Because BHA is oil-soluble, it can travel into the pore lining itself, making it the go-to choice for:
- Blackheads and clogged pores
- Oily and combination skin
- Mild inflammatory acne (salicylic acid also has anti-inflammatory properties on its own)
Popular Korean BHA products: COSRX BHA Blackhead Power Liquid (arguably the single most internationally famous Korean BHA product, largely due to K-beauty YouTube reviews around 2016-2018), Paula’s Choice-style dupes from Korean indie brands, Anua Heartleaf Pore Control Cleansing Oil (combines BHA-adjacent ingredients with cleansing oil for a double-cleanse-friendly pore treatment).
PHA: Best For Sensitive Skin and Beginners
PHAs are the newest category to gain traction in Korean skincare, largely as a response to consumer demand for gentler options. Because the molecules are physically larger, they exfoliate more slowly at the very surface layer of skin and don’t penetrate as deeply — which also means less risk of sun sensitivity, a known side effect of AHA use.
Best for:
- Rosacea-prone or very reactive skin
- First-time chemical exfoliant users
- Anyone who found AHA or BHA too irritating
Popular Korean PHA products: Neogen Bio-Peel Gauze Peeling Pads (some variants use PHA-forward formulations), various newer indie Korean brands increasingly blending PHA into “gentle glow” toners aimed at the growing “skinimalism” (미니멀 스킨케어) trend in Korea.
Can You Use All Three Together?
Using all three acid categories in the same routine, at full strength, at the same time is generally discouraged even by Korean brands that sell products in all three categories — it significantly raises the risk of over-exfoliation, barrier damage, and irritation. That said, some Korean multi-acid toners (like the Some By Mi AHA-BHA-PHA toner mentioned above) deliberately combine small amounts of all three at very low concentrations specifically so they can be used together safely as a single, gentle product, rather than layering three separate high-strength products.
If you’re building a routine from individual products rather than a pre-blended one, the safer approach is:
- Pick one primary chemical exfoliant based on your main concern (BHA for pores/oil, AHA for texture/dullness, PHA for sensitivity).
- Use it 2-4 times per week initially, monitoring for irritation.
- Only consider adding a second acid type once your skin has built tolerance, and even then, alternate days rather than layering them in the same session.
Sun Protection Is Non-Negotiable
All three acid categories increase photosensitivity to some degree, AHAs most significantly. This is a point Korean skincare culture takes especially seriously — daily SPF use, including reapplication, is treated as close to mandatory in Korean beauty routines regardless of weather or season, and this becomes even more critical when using any chemical exfoliant. Skipping sunscreen while using acids is one of the fastest ways to develop new hyperpigmentation rather than fade existing spots.
How to Introduce Chemical Exfoliants Into a Korean-Style Routine
Given the “thin to thick” layering logic of Korean routines, chemical exfoliants (in toner or essence form) typically slot in early, right after cleansing:
- Double cleanse (oil cleanser, then water-based cleanser)
- Chemical exfoliant toner (AHA/BHA/PHA)
- Hydrating toner or essence (often with soothing ingredients like Centella asiatica to buffer any irritation)
- Serum
- Moisturizer
- Sunscreen (AM only)
Frequently Asked Questions
Which acid should a complete beginner start with? PHA is the gentlest entry point, but if pore congestion or blackheads are your main concern, a low-concentration Korean BHA product (like the COSRX 0.5% BHA liquid) is specifically formulated to be beginner-friendly.
Can I use chemical exfoliants with retinol? It’s possible but requires caution — most dermatologists, including those frequently cited in Korean skincare media, recommend not using strong AHA/BHA and retinol on the same night, alternating instead (e.g., acids on odd nights, retinol on even nights).
How often do Koreans typically exfoliate chemically? Given the lower concentrations typical of Korean formulations, 2-4 times weekly is common, though some very gentle PHA toners are marketed for daily use.
Do I still need physical exfoliation (scrubs) if I use chemical exfoliants? Generally no — Korean skincare culture has moved fairly firmly away from physical scrubs in favor of chemical exfoliation, viewing scrubs as more likely to cause micro-tears and barrier damage than genuine benefit.
The Bottom Line
PHA, AHA, and BHA all exfoliate, but they do it through different mechanisms suited to different concerns — pores and oil for BHA, texture and dullness for AHA, and gentle surface renewal for PHA. Korean formulations tend to favor lower concentrations used more consistently over time rather than occasional high-strength treatments, which is a philosophy worth adopting regardless of which acid you choose to start with.