Glycolic Acid and AHAs: The Complete Guide

Glycolic acid is the most searched-for exfoliating ingredient in skincare and the headline name among AHAs. It is also easy to buy wrong: an "AHA toner" on the label need not contain any glycolic acid at all, and the same acid at 7% and at 21% calls for completely different regimens, so the percentage is the first thing to read.

What is glycolic acid, and why is it the flagship AHA?

AHAs (alpha hydroxy acids) are a family that includes glycolic, lactic, mandelic and a few related acids. Glycolic is chemically the simplest and smallest of them. Its INCI name is Glycolic Acid, and under that name CosIng, the European cosmetic ingredient database, records the function "buffering", i.e. regulating a product's pH. Everything else you read about it — peeling, glow, smoother texture — comes from the brands' own claims.

What does glycolic acid actually do for skin?

Summing up how the manufacturers we know first-hand describe it: glycolic acid loosens the bonds between dead cells on the skin's surface so they shed more easily. Beauty of Joseon says its AHA + BHA toner sweeps away dead skin cells and cleanses clogged pores; VT Cosmetics says its glycolic mist gently removes dead cells and bumps, leaving skin smooth and radiant; Heimish positions its serum as surface exfoliation. The sum of those claims is also the realistic expectation: smoother texture, a more even tone, more glow — with no promise to "cure" anything.

AHA, BHA and PHA — what's the difference, and which skin is each for?

In short, AHAs are water-soluble and work on the skin's surface — texture, tone, glow. BHA (salicylic acid) is oil-soluble, so it gets into pores — the usual pick for oily skin, and the subject of our separate guide to salicylic acid in skincare. PHAs have larger molecules, work more slowly and gently, and are often suggested as a first step for more sensitive skin. Many Korean formulas combine all three at low concentrations — convenient for combination skin that wants texture and pores handled by a single product.

Glycolic or lactic: when is gentler better?

Lactic acid is the second best-known AHA. Interestingly, CosIng records for it not only pH buffering but also the functions "humectant" (binding moisture) and "skin conditioning" — hence its reputation as the softer, more hydrating option. In practice formulators happily pair the two: Heimish declares 21% glycolic and 9% lactic acid in one formula for its RX AHA BHA Peeling Serum — glycolic carries the exfoliation, lactic rounds it out. If your skin is reactive, the sensible order of acquaintance is PHA or lactic first, glycolic later.

Percentages on the label: what do 7% and 21% actually mean?

The percentage is the most useful number a brand can publish — and it pays to buy where it is stated plainly. For orientation, three real examples with manufacturer declarations. Some By Mi AHA BHA PHA 30 Days Miracle Toner is the entry level: the brand lists mild acid doses in ppm — salicylic 100 ppm, lactobionic 100 ppm, citric 500 ppm. Note the lesson: an "AHA toner" does not automatically mean glycolic — here the AHA component is citric acid. The middle tier is 7% glycolic — in Korean beauty it is what VT Cosmetics declares for its glycolic face-and-body mist. The high tier is the Heimish RX AHA BHA Peeling Serum: 21% glycolic + 9% lactic — a rinse-off treatment the brand's own instructions cap at 10 minutes on skin, once or twice a week, in the evening, and explicitly address to experienced acid users.

Who is glycolic acid for — and who should ease in carefully?

It has the most to offer dull skin, uneven texture, visible pores and a tired-looking tone. Caution is due if your skin is sensitive, barrier-compromised or freshly irritated: pick the gentlest format and introduce it slowly. Beauty of Joseon recommends that sensitive-skinned users patch-test its toner for 24 hours before first use — a smart habit with any acid product. VT states outright that its mist must not go on wounds or damaged skin. And if pores and an oily T-zone are your main concern, read our salicylic acid guide before reaching for glycolic — BHA may be the more logical first pick.

How to introduce glycolic acid into a routine

The usual recommendation: start with a lower concentration and lower frequency, then build up gradually. The Korean approach to exfoliation typically picks one of two lanes: a mild acid toner used regularly, or a stronger peel once a week — not both at once. The first lane looks like Beauty of Joseon Green Plum Refreshing Toner AHA + BHA, a gentle green-plum toner the brand says to press in with hands or sweep on with a cotton pad after cleansing; the second lane lives in our peelings and enzyme powders category. Save the strong formulas for the evening: Heimish explicitly recommends its high-percentage serum at night.

SPF alongside acids

This is not a filler phrase — it is a standard warning printed on the products themselves. Beauty of Joseon carries a warning for its AHA + BHA toner: AHA may increase the skin's sensitivity to the sun and the risk of sunburn, so the brand instructs users to wear sunscreen and protective clothing and limit sun exposure — while using the product and for a week afterwards. VT similarly warns about possible reactions to direct sunlight after use. As long as acids are in your routine, morning SPF belongs to that same routine — pick yours from our sun protection category.

Glycolic acid with retinol, niacinamide and vitamin C

Retinol: the most common approach is to split them across evenings — acids one night, retinol the next, since both actives need an adjustment period. How to build that schedule is covered in detail in our guide to retinol in skincare. Niacinamide: it gets along with acids; VT's glycolic mist also contains niacinamide, listed for a brighter-looking skin finish, so clearly the two ingredients do not rule each other out. Vitamin C: in practice it has settled into the morning routine, with SPF on top, while acids take the evening; the two actives never meet on skin at the same time, and skin has fewer reasons to complain.

When to expect results — and what you'll feel at first

The first thing most people notice, often after the very first uses, is touch: skin feels smoother because the surface layer of dead cells is gone. A more even tone and faded dark marks are the slow category — that result is built over weeks of regular, moderate use, not by applying more and more often. Early on, a brief, mild tingle is possible. If instead you get redness that will not settle, swelling or itching, the sensible first move is a pause — and the manufacturers are unambiguous: Some By Mi and VT both instruct in their official directions to consult a specialist.

Glycolic acid for the body: keratosis pilaris, rough patches, ingrown hairs

Bumps on the upper arms (keratosis pilaris), rough backs and shoulders, cracked heels — all are zones where exfoliation earns its keep. The full-body format is best illustrated by VT Glycolic Reedle Shot Head To Toe Mist: the brand declares 7% glycolic acid, a 360° rotating nozzle for the back and shoulders, and use quite literally from head to toe — scalp and heels included. Regular gentle exfoliation is also the classic care for areas prone to ingrown hairs after hair removal — with the same rule as for the face: never on freshly damaged or irritated skin.

Home care or a chemical peel at the clinic: where is the line?

An in-clinic chemical peel and at-home acids share the chemistry but not the rules. Professional treatments use considerably higher concentrations and are performed under the supervision of a trained specialist who assesses the skin before, during and after — a conversation for your cosmetologist or dermatologist, not for a beauty shop's blog. Home products, even ones that sound as serious as Heimish's 30%-total-AHA formula, are designed for self-use under strict adherence to the instructions: limited time on skin, rinsing off, pauses between uses. The line is simple: anything beyond that is not "stronger home care" — it is a professional procedure.

Two questions before you buy

Toner, serum or peel — where should I start?

With the gentlest format: a low-dose acid toner after cleansing, a few times a week. A practical option dosage-wise is toner pads — pre-soaked discs that are hard to overdo. High-percentage serums and peels come later, once your skin already knows acids and you know exactly why you need something stronger.

Can I use glycolic acid during pregnancy?

The brands themselves are cautious here: Beauty of Joseon states that its toner's formula contains ingredients not recommended during pregnancy and breastfeeding, and recommends consulting a doctor before adding any new skincare product. The same goes for every acid product.

In closing

The percentage on the label and the frequency instructions say more than the word "AHA" itself: VT positions its 7% mist as a daily exfoliant, while Heimish caps its 21% serum at once or twice a week and at most 10 minutes on skin. If you are new to acids, start with a mild toner, save the stronger peels for the evening, and keep morning SPF in the routine for as long as acids are in it.