Glycolic acid, lactic acid, salicylic acid and gluconolactone are all chemical exfoliants, and each one behaves differently. This guide lays out their molecule sizes, where they act, the MFDS concentration limits, and the strengths and frequencies that keep them safe.
MFDS notices · Peer-reviewed clinical basis · Updated May 2026
Chemical exfoliants are acidic ingredients that loosen the bonds between dead skin cells so the cells can shed. They fall into three broad groups, alpha hydroxy acid (AHA), beta hydroxy acid (BHA) and polyhydroxy acid (PHA). Each has its own molecule size, solubility and site of action. This guide draws on the notices of Korea's Ministry of Food and Drug Safety (MFDS) along with peer-reviewed clinical data.
The three groups at a glance
Group
Key ingredients
Characteristics
Main site of action
AHA
Glycolic, lactic, mandelic, citric acids
Water-soluble, surface action
Surface dead cells
BHA
Salicylic acid
Oil-soluble, gets into pores
Sebum and debris inside pores
PHA
Gluconolactone, lactobionic acid
Water-soluble, large molecule
Surface (low irritation)
AHA — alpha hydroxy acid
An alpha hydroxy acid (AHA) is a water-soluble acid that loosens the bonds between surface dead cells so they slough off. How deep it goes and how much it stings depend on the size of the molecule.
The main AHA ingredients
Ingredient
Source
Molecular weight
Profile
Glycolic acid
Sugar cane
76 (smallest)
Clear action, deep penetration
Lactic acid
Lactic bacteria, milk
90
Medium strength, comes with hydration
Mandelic acid
Almonds
152
Large molecule, low irritation
Citric acid
Citrus fruit
192
Mostly used as a pH adjuster
MFDS limits (voluntary management standard)
Glycolic acid is used up to 10% in cosmetics, with a recommended pH of 3.5 or higher.
Lactic acid is used up to 5% in cosmetics, with a recommended pH of 3.5 or higher.
Everyday toners and serums commonly land at 5 to 10%.
High-strength peels at 20 to 30% are reserved for quasi-drugs or medical settings.
Skin becomes more sensitive to sunlight after AHA use. The MFDS requires the label note "use products containing AHA together with sunscreen" (Guidelines on Cosmetic Labeling and Advertising). Before time outdoors, skip the AHA or be sure to use an SPF 50+ sunscreen.
BHA — beta hydroxy acid (salicylic acid)
A beta hydroxy acid (BHA) is an oil-soluble acid. It dissolves into sebum and reaches inside the pore to break down trapped oil and dead cells. In cosmetics, BHA effectively means salicylic acid.
MFDS concentration limits
Everyday cosmetics: used at 0.5 to 2%.
Quasi-drugs (acne soaps and the like): allowed up to 6%.
Medical peels: used at 20 to 30% in clinical settings.
Characteristics
Because it dissolves into oil, it helps with oily, congested pores and areas prone to acne.
It belongs to the salicylate family, like aspirin, and has a mild anti-inflammatory action.
It tends to raise light sensitivity less than AHA does, but sunscreen is still recommended.
High concentrations are best avoided during pregnancy (FDA guidance).
PHA — polyhydroxy acid (the third generation)
A polyhydroxy acid (PHA) is chemically similar to AHA but has a larger molecule with several hydroxyl groups that like water. That makes it slower to penetrate and gentler on skin.
The main PHA ingredients
Gluconolactone: a molecular weight of 178, with antioxidant action alongside.
Lactobionic acid: a molecular weight of 358, with strong water-binding that gives a hydrating effect.
Characteristics
It can suit sensitive skin and people with eczema or rosacea.
It is gentler than AHA, though it also works more slowly.
Cosmetic concentrations usually sit at 4 to 10%.
Why pH matters
How well AHA and BHA work depends not only on concentration but heavily on pH, the level of acidity. A lower pH means a higher share of free acid available to react, so the effect is more pronounced and the irritation rises right along with it.
pH range
Profile
pH 2.5 to 3.5
Strong (quasi-drugs, some high-strength toners)
pH 3.5 to 4.0
Standard (most cosmetics)
pH 4.0 to 5.0
Mild (PHA, sensitive skin)
As a rule, the MFDS recommends a pH of 3.5 or higher. Products below that can be more irritating, so cut the frequency and always patch test first.
Low strength (0.5 to 2% BHA, 5% AHA, PHA): used daily or every other day.
Medium strength (5 to 7% AHA): used two or three times a week.
High strength (10%+ AHA, quasi-drugs): used once or twice a week at most.
The standard approach is to start at the lowest frequency and build up gradually, watching for irritation, redness or peeling along the way (AAD guidance).
Layering — using acids with other actives
Combination
Recommendation
AHA/BHA + vitamin C
Not in the same step. Vitamin C in the morning, AHA/BHA at night.
AHA/BHA + retinol
Alternate on different days. Used together, irritation stacks up.
AHA/BHA + niacinamide
Workable. Leaving a gap (15 minutes or more) is safer still.
AHA/BHA + sunscreen
Essential. Strong sun protection is advised the day after using AHA/BHA.
Editorial Tip
Frequency over strength
"Jumping to a stronger acid because exfoliation feels slow is a trap. Sticking with the same strength for four to six weeks while protecting the skin barrier tends to lead to smoother skin in the end."
— Beauty Dupe Editorial
Frequently asked questions
"Is it fine to use a BHA every day?"
A low strength of 0.5 to 2% can generally be used daily or every other day. When you first start, though, it is safer to go every other day until your skin settles, then build up to daily.
"Do acids make skin thinner?"
At a sensible strength and frequency, only the surface layer of dead cells is normalized and the deeper dermis is left alone. In fact, glycolic acid used moderately over the long term has been reported to support collagen synthesis. Pushed too hard at high concentrations, though, it can damage the surface layer.
"Is it safe to use during pregnancy?"
Low-strength AHAs such as 5 to 7% glycolic acid or 5% lactic acid are generally classed as safe. Salicylic acid at a cosmetic strength of 2% or below is considered relatively safe for topical use, while ACOG advises avoiding high concentrations. For the full picture, see our pregnancy and breastfeeding guide.
"If exfoliation feels too slow, should I move to something stronger?"
No. Using a strong acid often can weaken the skin barrier and actually lead to more breakouts. Steady use at a set frequency tends to help, so reassess after four to six weeks.
Skin Warning
Skin is more sensitive to sunlight after AHA use. Apply an SPF 50+ sunscreen whenever you go out, and when you first start, begin at once or twice a week in the evening, then build up the frequency as you watch how your skin reacts.
Sources
Korea Ministry of Food and Drug Safety, "Regulation on Cosmetic Safety Standards" — AHA and BHA concentration limits
Korea Ministry of Food and Drug Safety, "Guidelines on Cosmetic Labeling and Advertising" — mandatory AHA sun-caution label
U.S. FDA — Alpha Hydroxy Acids Safety Information
Tang SC, Yang JH. "Dual Effects of Alpha-Hydroxy Acids on the Skin." Molecules. 2018
American Academy of Dermatology — Chemical Exfoliation Guide
Disclaimer · This guide is general information and does not replace a personal diagnosis. If irritation, redness or peeling occurs, stop use right away, and see a dermatologist if the problem persists.
