Buy your first acid toner and one question hits right away. What strength should I pick, and how often do I use it? The ingredient list never shows the percentage, which makes it harder. This guide is for first-time acid users. It covers which acid to start with, how to read strength from the label, and how to build up over the first few weeks.
MFDS notices · Peer-reviewed clinical basis · Updated October 2026
Exfoliating acids come in three groups: AHA, BHA and PHA. All of them loosen the bonds between dead skin cells so old buildup sheds on its own. What AHA and BHA are and how they differ is covered in depth in our AHA and BHA ingredient guide. Here we stick to the practical side: which acid to start with, at what strength, and how often.
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)
For a first acid, you only need one pick from this table. Pores bothering you? Go with BHA. Texture and dryness? AHA. Worried your skin is too sensitive? Start with PHA. The skin type table further down breaks this out in more detail.
AHA: Korea uses warning labels instead of a cap
Surprisingly, Korea sets no maximum for how much AHA a cosmetic can contain. Instead, products above certain levels must carry warning text on the label. Those warnings are your clue to a strength the ingredient list never shows.
A product with more than 0.5% AHA must tell you to use sunscreen with it.
Above 10%, or below pH 3.5, the label also has to tell you to consult a specialist. If the rules are followed, seeing that line means you are holding a strong product, so skip it for now.
The expert panel (CIR) guidance the FDA cites also sets 10% or less at pH 3.5 or higher for everyday cosmetics.
High-strength peels at 20 to 30% are a dermatology clinic treatment, not a home product.
Your skin is more sensitive to UV while you use AHA. In one study, skin treated with 10% glycolic acid reddened more easily under UV. That is the reason the MFDS made the warning mandatory. Before a long day outdoors, like the beach or a hike, skip the AHA or wear an SPF 50+ sunscreen with care.
BHA (salicylic acid): MFDS concentration limits
Unlike AHA, BHA does have fixed limits in Korea. That is why the strength of an imported product and a Korean one can differ.
Leave-on cosmetics: up to 0.5%. The notified amount for acne-care functional cosmetics is also 0.5%.
Rinse-off products: up to 2% in body cleansers and 3% in rinse-off hair products. It cannot be used for anything else.
Medical peels: used at 20 to 30% in clinical settings.
In practice, a BHA toner or serum bought in Korea is 0.5% or less. The 2% products common abroad have four times that concentration, so a Korean product is the easier place to start. BHA raises sun sensitivity less than AHA does, but wear sunscreen all the same.
PHA: for first-timers and sensitive skin
A polyhydroxy acid (PHA) behaves much like AHA but has a far bigger molecule. It carries several water-loving parts (hydroxyl groups), so it sinks in slowly. The result is gentle action with less irritation. Some call it the third generation of acids.
Gluconolactone: a molecular weight of 178, with antioxidant action alongside.
Lactobionic acid: a molecular weight of 358, with strong water-binding that helps hydrate.
People with sensitive skin, eczema or rosacea can often use it with little trouble. It also works more slowly, so patience matters. Cosmetic concentrations usually sit at 4 to 10%.
It is more common in Korean products than you might think. Of the 2,426 full ingredient lists in our database, 171 include gluconolactone. That is about four times the 41 that include glycolic acid. Lactobionic acid appeared in 12. On a label, look for Gluconolactone and Lactobionic Acid.
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Why pH matters
Two products at the same 10% can feel very different depending on pH, the level of acidity. A lower pH means a bigger share of the acid is free to work. The effect gets stronger and so does the irritation.
pH range
Profile
pH 2.5 to 3.5
Strong (peels, some high-strength toners)
pH 3.5 to 4.0
Standard (most cosmetics)
pH 4.0 to 5.0
Mild (PHA, sensitive skin)
As covered above, an AHA product below pH 3.5 must carry the consult-a-specialist warning. If you use one, apply it less often and always do a patch test first (try it behind the ear or on the inner arm and watch for a reaction).
Your first acid by skin type
Starting from your skin type narrows things down fast. Find your skin on the left and just avoid what is in the right column.
Safe frequency of use: building up over the first weeks
With acids, raising the frequency slowly matters far more than picking a strong one. Once your skin has adjusted, these are rough targets by strength.
Low strength (0.5 to 2% BHA, 5% AHA, PHA): daily or every other day.
Medium strength (5 to 7% AHA): two or three times a week.
High strength (10%+ AHA): no more than once or twice a week.
You do not start at those numbers, though. The American Academy of Dermatology also advises beginning at the lowest frequency and building up slowly while you watch for stinging, redness or peeling. For example, use it once or twice in the first week, evenings only. If nothing flares, move to every other day. If that still feels fine, a low strength can go daily. If a reaction shows up, step back one stage.
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Routine order: acids go on at night, right after cleansing
An acid toner or pad usually goes on right after you wash your face and pat it dry. Follow with serum and cream to put moisture back, and you are done. Keep it to your evening routine at first, and finish the next morning with sunscreen as the last step. The full step order is in our skincare layering order guide.
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 days. For example, acids on Monday, Wednesday and Friday, retinol on Tuesday, Thursday and Saturday, and a rest on Sunday. On the same night, 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
"Switching to a stronger acid because exfoliation feels slow is the most common mistake. Staying on the same strength for four to six weeks and protecting your skin barrier is the quicker road to smoother skin."
— Beauty Dupe Editorial
Frequently asked questions
"Is it fine to use a BHA every day?"
At a low strength of 0.5 to 2%, daily or every-other-day use is generally fine. Still, start every other day and move to daily once your skin has clearly adjusted.
"Do acids make skin thinner?"
At a sensible strength and frequency, acids clear only the dead cells on the surface and leave the deeper dermis alone. Glycolic acid used moderately over the long term has even been reported to support collagen production. The trouble starts when you use a high strength too often, which 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. ACOG considers over-the-counter salicylic acid and glycolic acid products fine during pregnancy if needed. The American Academy of Dermatology also sees short-term, low-strength products as generally fine. Save high-strength peels for after delivery. 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. Keep using what you have at a steady pace and judge it after four to six weeks.
Skin Warning
If stinging, redness or peeling lasts for days, drop the frequency one step. While you are using acids, SPF 50+ sunscreen is a given whenever you go out.
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.
