AHAs, BHAs, and PHAs are three families of chemical exfoliants that remove dead skin cells without scrubbing. The key difference: AHAs work on the surface for dry skin, BHAs penetrate pores for oily and blemish-prone skin, and PHAs offer gentle exfoliation ideal for sensitive skin.
If you're wondering which one to choose without irritating your skin, you've come to the right place. We'll explain the mechanisms, the profiles suitable for each acid, and how to integrate them into a practical Korean routine.
Are you looking directly for Korean exfoliants with AHA, BHA, or PHA? The Some By Mi range is one of the most comprehensive on the subject, with formulas proven over 30 days. (see the Some By Mi selection)
What exactly is a chemical exfoliant? ✨
A chemical exfoliant dissolves the bonds between dead cells on the surface to accelerate cell renewal. Unlike physical scrubs (grains, brushes), there is no friction, which reduces the risk of irritation and micro-lesions.
AHAs, BHAs, and PHAs belong to the same family of hydroxy acids, but they have different molecular sizes, penetration depths, and indications. In South Korea, these active ingredients have been integrated into routines since the 2000s via exfoliating toners (like the COSRX AHA/BHA Clarifying Treatment Toner) and targeted serums. Today, more than 60% of K-Beauty bestsellers for blemish-prone skin contain at least one of these acids.
The basic rule: using the right acid at the right time avoids irritation. Using two at the same time without a precise protocol is the first mistake of beginner K-Beauty routines.
AHAs: for dry skin seeking radiance 💧
AHAs (alpha-hydroxy acids) are water-soluble acids. They act on the surface of the epidermis by dissolving the "cement" between dead cells, without penetrating the pores.
The three most used AHAs in K-Beauty are glycolic acid (derived from sugarcane, the most penetrating AHA due to its small molecular size), lactic acid (milk fermentation, larger molecule, more superficial and hydrating action), and mandelic acid (almond origin, antibacterial, recommended for combination skin with mild blemishes).
AHAs are particularly recommended for dry, dull skin or skin with hyperpigmentation. Clinical studies published in the Journal of the American Academy of Dermatology confirm that lactic acid simultaneously improves skin hydration and exfoliation, making it a versatile active ingredient. Source: Smith W.P., JAAD (1996)
Expert tip: Many people overload with glycolic acid from the start. This is the most common pitfall with AHAs: their small molecular size makes them very effective, but also more irritating on unaccustomed skin. Start with lactic or mandelic acid, twice a week, before increasing frequency.
BHAs: the essential ally for oily and blemish-prone skin 🌿
BHAs (beta-hydroxy acids) are oil-soluble, meaning they penetrate pores by passing through sebum. Salicylic acid, at 1 to 2% concentration, is the only BHA used in cosmetics.
Its action is threefold: it exfoliates the surface of the epidermis, unclogs blocked pores (blackheads, comedones), and has a targeted anti-inflammatory action on painful pimples. It is this ability to act inside the pore that radically distinguishes it from AHAs. A review published in Clinical, Cosmetic and Investigational Dermatology (Arif T., 2015) confirms its effectiveness on mild to moderate acne. Source: CCID
In K-Beauty, salicylic acid at 0.5-2% appears in exfoliating toners, targeted serums, and cleansers for oily skin. The COSRX BHA Blackhead Power Liquid (with 4% betaine salicylate, a milder functional equivalent) is one of the most popular products in this category.
Ideal profile for BHAs: combination to oily skin, acne-prone, enlarged pores, recurrent blackheads. Note: salicylic acid is not recommended during pregnancy and breastfeeding.
PHAs: gentle exfoliation for sensitive and reactive skin 🪷
PHAs (poly-hydroxy acids) have a larger molecular size than AHAs and BHAs. As a result, they do not penetrate as deeply into the epidermis, making them suitable for sensitive, atopic, or reactive skin.
The three main PHAs in cosmetics are gluconolactone (antioxidant, anti-inflammatory), galactose (stimulates collagen production), and lactobionic acid (strong hydrating power). Their exfoliating efficacy is real but more gradual, over 4 to 6 weeks of regular use.
PHA is also the most tolerated acid by skin prone to redness or reactivity to classic AHAs. In K-Beauty, it is often combined with centella asiatica to strengthen the skin barrier during exfoliation, particularly in Some By Mi and Skin1004 ranges.
Comparative table: AHA, BHA, PHA at a glance 🔎
| Acid | Solubility | Area of action | Ideal skin type | Key active ingredients | Beginner frequency |
|---|---|---|---|---|---|
| AHA | Water-soluble | Epidermal surface | Dry, dull, spots | Glycolic, lactic, mandelic | 2 times/week |
| BHA | Oil-soluble | Surface + inside pores | Oily, acne-prone, enlarged pores | Salicylic acid, betaine salicylate | 2 to 3 times/week |
| PHA | Water-soluble | Surface (gradual action) | Sensitive, reactive, atopic | Gluconolactone, galactose, lactobionic | 3 to 4 times/week |
AHA and BHA together: good or bad idea? ⚠️
Combining AHA and BHA in the same routine is possible, but requires a precise protocol. The most common pitfall is to apply them at the same time on unaccustomed skin, which causes redness, flaking, and increased sensitivity.
The K-Beauty rule for blemish-prone skin that wants both effects: use BHA in the morning (or evening depending on the formula) and alternate AHA in the evening, never on the same day during the introduction phase. Once the skin is accustomed (4 to 6 weeks), some Korean products combine both in a single formula, notably the Some By Mi AHA BHA PHA 30 Days Miracle Toner, which combines the three acids at low concentrations for a synergistic and less aggressive action.
What should never be combined on the same day without precaution: AHA or BHA with retinol, high-concentration niacinamide (>10%), or pure vitamin C (ascorbic acid). These combinations can disrupt skin pH and weaken the barrier.
If you're new to chemical exfoliants in K-Beauty, the article on our review of COSRX provides concrete benchmarks for entry-level salicylic acid formulas.
How to integrate chemical exfoliants into a Korean routine? 🌸
In a K-Beauty routine, chemical exfoliants are applied after cleansing and before serum, in the form of an exfoliating toner or a specific serum. Here is the application order according to skin type:
Dry or dull skin: gentle cleanser in the evening, then AHA toner (lactic or mandelic acid), moisturizer with ceramides. Use the exfoliating toner 2 to 3 evenings a week, not every evening.
Oily or acne-prone skin: double cleansing, then BHA toner (salicylic acid or betaine salicylate), light serum, non-comedogenic cream. BHA can be used morning or evening depending on the formula. Always apply SPF 50 in the morning, regardless of the season, as exfoliating acids increase sun sensitivity.
Sensitive skin: sulfate-free cleanser, PHA toner (gluconolactone or lactobionic), repairing cream. PHAs can be used more frequently because their action is gentler, but starting 3 times a week is still recommended.
For sensitive skin that still wants the benefits of more targeted exfoliation, Anua products often integrate heartleaf-based exfoliants combined with gentle concentrations of AHAs, making them a more accessible entry point. The Anua review details recommended formulas according to concerns.
Realistic timelines: when do you see results? ⏱
The results of chemical exfoliants are not immediate. Here are the observed timelines depending on the active ingredient and regularity of application:
- AHA (radiance, texture): first visible effects within 2 to 3 weeks of regular use. Lasting results on hyperpigmentation spots in 8 to 12 weeks.
- BHA (pores, blemishes): visible reduction of comedones and blackheads in 4 weeks. Mild inflammatory acne shows improvement after 6 to 8 weeks.
- PHA (texture, sensitivity): improved texture in 4 to 6 weeks. The effect is gradual but cumulative.
Consistency takes precedence over concentration. A 1% BHA used 3 times a week for 8 weeks gives better results than a 2% BHA used excessively for 2 weeks with resulting irritation.
Key takeaways 📌
To choose between AHA, BHA, and PHA, there are three essential points. First, your skin type is the number one criterion: dry or dull skin, choose an AHA; oily and blemish-prone skin, go for a BHA; sensitive skin, start with a PHA. Second, frequency is as important as concentration, especially at the beginning. Finally, regardless of the acid family chosen, SPF 50 in the morning is mandatory to protect skin weakened by exfoliation.
If you're unsure of your skin type before choosing, the Holy Skin free skin diagnosis guides you in 2 minutes towards the active ingredients suited to your situation. You can also directly explore the available Korean exfoliants selected for each skin profile.
