Ingredient

Glycolic Acid

The smallest and fastest exfoliating acid. It works quickly on rough texture and dull, uneven skin, and it stings the most.
Dr. Schwarz, MD · Board-certified dermatologistLast reviewed September 8, 2026
Four glycolic acid toner and liquid bottles lined up on white, one with its box

Start here

Glycolic acid is what most people mean when they say acid. It has the smallest molecule in its family, so it gets into skin fastest, which is why it smooths rough, dull skin quickest and turns skin red and sore quickest if you overdo it. The mistake I correct most often is frequency — people use a 10% serum every night, layer a retinoid on top, and arrive with a tight, stinging face they think is progress. Two or three nights a week is enough for most skin, daily sunscreen comes with it, and if your skin is sensitive or marks dark after irritation, I start people on lactic or mandelic acid instead.

— Dr. Schwarz, Board Certified Dermatologist

Key Facts

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Also calledAHA, alpha hydroxy acid, hydroxyacetic acid
TypeAlpha hydroxy acid (AHA), exfoliates the surface of the skin
Strengths soldRoughly 5% to 10% in leave-on skincare. Much higher concentrations are used for professional peels.
UseAt night, two or three times a week for most people
Time to workAbout 2 weeks for texture, 8 to 12 weeks for tone and marks
Prescription neededNo at skincare strengths. Stronger peels are done by a trained professional.

What It Is

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Glycolic acid is an alpha hydroxy acid, usually shortened to AHA, a family of small acids first identified in foods. It comes from sugar cane, though the skincare version is made in a lab so strength and purity are consistent. It is the smallest molecule in the family, and size matters, because smaller molecules cross the surface more easily. So it acts faster than its relatives and is more likely to sting. Leave-on skincare sits between 5% and 10%. Stronger solutions are professional peels, left on a set number of minutes and then neutralized. A peel and a serum are different treatments, not the same product used differently.

How It Works

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The dead cells at the surface of your skin are held together by protein bonds, a bit like stitching. Glycolic acid loosens it, so the oldest cells let go and shed instead of piling up. The pile-up reads as rough, flaky or dull skin, so smoothness is usually the first thing people notice.

Clearing that layer has knock-on effects. Pigment sits inside the surface cells, so shedding them faster lightens flat brown marks left by spots and sun. Pores clog less easily when the lining is not shedding into a plug. Over months there is reasonable evidence AHAs increase collagen underneath, which is why glycolic acid appears in products for fine lines.

How much happens depends on three things — the percentage, the pH, and how long it stays on the skin. That is why glycolic acid in a cleanser does very little. The contact time is seconds.

The downside is the same mechanism running too far. Take too much off, too often, and skin goes red, tight and sore, losing water faster than it can replace it. It also makes skin more sensitive to sunlight, and that lasts about a week after you stop.

Here is where Glycolic Acid acts in the skin, and what the others do instead.

About Glycolic Acid
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Skin basics
LOOSENS DEAD SKINSTAYS ON THE SURFACEPULLS WATER INPULLS WATER INSEALS WATER INSEALS WATER INFILLS THE GAPSFILLS THE GAPS

These acids work at the surface. They break the bonds holding dead cells to each other, so the top layer sheds more evenly. Skin looks smoother and brighter, and anything applied afterwards gets in more easily. The smallest of these acids, so it goes deepest and stings most.

Glycolic acid is the smallest of the acids, which is why it is also the most stinging: it moves through the outer layer fast. It works there, loosening the bonds between dead cells, and does not need to go deeper.

A humectant draws water into the outer layer and holds it there. Skin holding more water is plumper and more flexible, and fine lines caused by dryness soften within minutes. Seal it with something on top or in dry air the water can simply evaporate away.

A humectant draws water into the outer layer and holds it there. Skin holding more water is plumper and more flexible, and fine lines caused by dryness soften within minutes. Seal it with something on top or in dry air the water can simply evaporate away.

An occlusive sits on the surface and slows water escaping. It adds nothing to the skin; it stops what is already there from leaving, which is why it works best over damp skin.

An occlusive sits on the surface and slows water escaping. It adds nothing to the skin; it stops what is already there from leaving, which is why it works best over damp skin.

Emollients are oils and lipids that sit in the spaces between the cells of the outer layer, the mortar between the bricks. They fill those gaps rather than covering them over, so skin feels smoother straight away, water stays in and irritants stay out.

Emollients are oils and lipids that sit in the spaces between the cells of the outer layer, the mortar between the bricks. They fill those gaps rather than covering them over, so skin feels smoother straight away, water stays in and irritants stay out.

The outermost layer, and the one every moisturizer is aiming at. It is dead — flattened cells stacked like bricks, with a mix of fats as the glue between them. That glue is what holds water in and keeps irritants out.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

What It Treats

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Ingrown Hairs

Moderate evidence

A leave-on lotion or toner used two or three times a week keeps the follicle openings clear, which is the point where a curved hair gets stuck. It also helps the flat dark marks fade. Use it on days you do not shave, because acid on freshly shaved skin stings and adds irritation.

Keratosis Pilaris

Keratosis Pilaris

Moderate evidence

Loosens the dead cells stuck at the surface, which smooths the skin around the bumps. It is the most likely of the acids to sting and to leave the skin pink, so it suits the arms and thighs better than the cheeks. On deeper skin tones, build up slowly, because irritation is what leaves the dark marks.

Wrinkles and Fine Lines

Wrinkles and Fine Lines

Moderate evidence

Regular low-strength use smooths surface texture and softens fine lines, and it helps the dull, uneven look that goes with them. It reaches the outer layers only, so deeper creases and folds are untouched. Used on the same nights as a retinoid it usually causes more irritation than either is worth, so alternate them.

Close-up of the lower cheek, nose and mouth of a young person with medium-brown skin, turned three-quarters away from the camera against a pale blue background. Scattered flat dark brown marks are spread across the cheek, with a few small raised spots still active among them.

Post-Inflammatory Hyperpigmentation

Moderate evidence

Loosens the pigmented cells at the surface so they shed sooner, which helps brown marks more than gray ones. A low-strength product two or three nights a week is plenty. Stacking it with a retinoid on the same night is the classic way people end up red and peeling, which adds inflammation and slows everything down.

Not the Best For

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Milia

Limited evidence

Keeps the surface layer shedding evenly, on the same prevention logic as salicylic acid. Low strength only. Strong glycolic peels are the opposite of helpful here — deep peeling is one of the recognized causes of milia in the first place.

Sun Spots (Solar Lentigines)

Sun Spots (Solar Lentigines)

Limited evidence

Loosens the pigmented cells at the surface so they shed sooner, which lifts a little color out of a spot over months. It works better as the thing that helps a lightening cream get in than as a treatment on its own. Used too often it leaves skin irritated and more sun-sensitive, which on this page is exactly the wrong direction.

Forms

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The format sets the real dose more than the percentage does. A pad you wipe on and leave is a far bigger exposure than a cleanser rinsed off after twenty seconds, even at the same 10%. Two things on the label matter — the percentage, and whether it says buffered or partly neutralized, meaning the pH is raised and the product milder.

A row of Glycolic Acid products sold as toner or liquid, photographed on white.
Where most people start
Toner or liquid
Swept on with a cotton pad after cleansing. Usually 5% to 10%, and easy to control.
A row of Glycolic Acid products sold as serum, photographed on white.
Leave-on strength
Serum
Thicker, stays put, and the format for the higher percentages. The most likely to sting.
A row of Glycolic Acid products sold as pads, photographed on white.
Neck, chest and back
Pads
Pre-soaked and quick to sweep over areas a dropper cannot reach.
A row of Glycolic Acid products sold as body lotion, photographed on white.
Rough arms and legs
Body lotion
Higher strengths in a moisturizing base. Skin below the neck takes far more than the face.
A row of Glycolic Acid products sold as wash-off peel, photographed on white.
Once a week
Wash-off peel
Left on for minutes, then rinsed. The lowest-commitment way to try a strong percentage.

Strengths

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The useful home range is narrow. When a product has not worked, contact time or consistency is the answer more often than a higher number.

WeakestStrongest
Under 5%5% to 10%20% to 30%50% to 70%
Everyday
Under 5%
Cleansers, daily toners and body lotions. Mild enough to use often.
The standard leave-on range
5% to 10%
What most serums and treatment pads use. Ten percent is the usual home ceiling.
Light professional peel
20% to 30%
Applied in a clinic for a few minutes, then neutralized, usually as a course.
Deeper professional peel
50% to 70%
Trained hands only. Longer recovery, and a real risk of lasting pigment change.

Basics

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When to Apply
At night, on clean dry skin, before moisturizer. Wait a minute or two after washing, because damp skin stings more.
How to Start
Two nights a week for the first two weeks, then build up only if your skin stays comfortable. Most people settle at two or three nights a week. Nightly use is not the goal.
If It Irritates
A short sting on application is common. Redness, tightness or flaking still there the next day is not. Cut back to once a week, apply moisturizer first, or move to a gentler acid.
If It’s Not Working
Give it eight to twelve weeks for tone and marks. Before raising the strength, check the contact time — glycolic acid in a cleanser is probably the problem. Daily sunscreen is not optional here, because it increases how easily you burn and because sun re-darkens the marks you are fading.

Sample Routine

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Here is where Glycolic Acid sits in a day, and what goes around it. Pick what you are treating and what your skin is like, and the rest of the routine changes to suit.

What to Expect

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Nights 1 to 3 | Adjusting
A sting or warmth for a minute or two, sometimes pinkness.
Weeks 1 to 2 | Working
Skin feels smoother and looks less dull. Light flaking is normal; sheets of peeling mean the product is too strong or too frequent.
Weeks 4 to 8 | Building
Tone evens out and flat brown marks begin to lighten.
After 12 weeks | Judge it here
If tone and texture have not moved with consistent use and sunscreen, change product or ingredient.

What to Avoid

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  • A dose problem, not a conflict Almost everything that goes wrong with glycolic acid comes from using too much, too often.
  • Using it every night at the start The most common mistake by far. More often stops helping sooner than people expect.
  • Layering it with a retinoid In the same routine. Both loosen the surface layer, and together they produce a red, stinging face. Alternate nights.
  • Scrubs, brushes and rough cloths Physical scrubbing on top of chemical exfoliation causes most acid injuries.
  • Skipping sunscreen Glycolic acid makes skin burn more easily, and that lasts about a week after you stop. Not negotiable.
  • Broken, sunburned or freshly waxed skin Wait until the skin is intact, and leave it out several days either side of waxing, threading or laser.
  • Leaving a home peel on too long Longer than the label says. Those times are set for a reason, and ignoring them causes chemical burns.

If You Stop

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Texture goes back first. Within a few weeks the surface layer builds up again, and skin feels rougher and looks duller than it did while you were using it. Pigment behaves differently. Marks that have already faded stay faded, because those pigmented cells were shed rather than switched off. What you lose is the steady removal of new pigment, so future marks sit around longer. No rebound and no withdrawal. Skin returns to its own baseline rather than getting worse. Plenty of people use it in courses, a few months on when tone bothers them and then a break.

Ask Your Doctor

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If you are pregnant or breastfeeding
Ask the doctor managing your pregnancy first.
If you have melasma
Exfoliating acids sit inside a larger plan, and used carelessly they can darken it.
If redness is still there the next day
That is more than you should expect.
If new dark or pale patches appear
On treated skin, especially on deeper skin tones, and after a peel.
If you already use another acne treatment
A prescription retinoid, benzoyl peroxide or an antibiotic. Ask how to fit an acid around it.
If you have eczema or rosacea
Or a damaged barrier. Let the skin settle first.
If you have blistering or a burn
After a peel, that needs looking at. Stop rather than treating it at home.

How It Compares

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Five lactic acid serums lined up on white, from The Ordinary, Glytone, Paula's Choice and Prequel16:9 hero for Lactic Acid. Never cropped: the tone strip and the corner logo depend on the full frame.

Lactic acid

The same

A larger molecule, so it works more slowly and stings less, and it holds water in the skin while it exfoliates. Glycolic acid acts faster on rough texture.

Five mandelic acid serums and their boxes lined up on white with clear gel swatches16:9 hero for Mandelic Acid. Never cropped: the tone strip and the corner logo depend on the full frame.

Mandelic acid

The same

The gentlest of the common AHAs and less likely to irritate skin into making dark marks. It is slower, and much less studied.

Five PHA toner and serum bottles lined up on white with clear liquid swatches beside them16:9 hero for Polyhydroxy Acids (PHAs). Never cropped: the tone strip and the corner logo depend on the full frame.

Polyhydroxy acids

Worse

Considerably gentler, hydrating, and they have not been shown to increase sun sensitivity. They also do less, more slowly.

Paula's Choice 2% BHA exfoliant, La Roche-Posay Effaclar cleanser and a CeraVe psoriasis cream pumpLabeled cutaway diagram of a single skin pore, headed Salicylic Acid. The epidermis is a brick-textured band across the top and the dermis is pink below it, with a yellow oil gland at the base of the pore and a small cluster of bacteria inside it. A single dark navy callout line points into the top of the pore: decreases dead cells in pore. There are no other callouts, so the drawing shows one effect where the other ingredient diagrams show two or three.

Salicylic acid

Different job

Oil-soluble, so it works inside the pore, which makes it a better fit for blackheads and acne. Glycolic acid does more for surface tone and texture.

Retinoids

Different job

They work deeper and do considerably more for fine lines and acne over time, but they take longer, need a prescription at higher strengths, and are stopped in pregnancy.

Professional glycolic peel

The same

Same ingredient at much higher strength, with a short contact time and someone trained watching the skin. Faster, and with a higher risk of pigment change.

Physical scrubs

Worse

Cheaper and instant, but the result is surface polish only, and scrubbing is a common cause of irritation.

Myths

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  • “If it stings, it is working.” Stinging tells you the acid has reached living skin, nothing about the result. Stinging that keeps happening means it is too strong or too often.
  • “A higher percentage always works better.” Strength is one of three things that decide what a product does; pH and contact time matter too. A good 8% serum can outperform a bad 15% one.
  • “Glycolic acid thins your skin.” It removes dead cells from the top layer, which rebuilds. Over months, AHAs are associated with a thicker living layer.
  • “You have to peel to get a result.” Visible peeling is a side effect, not the mechanism. Most people who do well never peel.
  • “Acids and vitamin C can never be used together.” Many products contain both. A comfort question, not a safety one. If it stings, separate them by time of day.
  • “It is only for light skin.” Glycolic acid is used on all skin tones. What changes on deeper skin tones is the margin for irritation — a reason to go slower, not to avoid it.

Questions Patients Ask

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How often should I use glycolic acid?

Two or three nights a week suits most people, and building up slowly matters more than where you end. Nightly use is not a target, and getting there costs more in irritation than it returns. Body skin tolerates more than the face.

Can I use it with retinol or tretinoin?

Yes, but not in the same routine when you are starting out. Both loosen the surface layer, and together they are the fastest way to a red, stinging face. Alternate nights. Once your skin is settled on both, some people combine them, which is a conversation for your dermatologist.

Is glycolic acid safe in pregnancy?

Very little is absorbed through the skin and it is commonly used, but this is not a decision to make from a webpage. Ask the doctor managing your pregnancy.

Will it fade my dark marks?

It fades marks, not scars. Flat brown or purple patches left by healed spots and sun lighten over roughly two to three months, provided you wear sunscreen daily. Indented or raised scars are structural and need in-office work.

Is glycolic acid a bad idea on deeper skin tones?

No, but the margin is narrower. Irritation triggers dark marks, so the risk comes from using it too strong or too often rather than from the ingredient. A lower strength, twice a week, with daily sunscreen and a moisturizer. Mandelic acid and PHAs are alternatives.

What is the difference between glycolic, lactic, mandelic and PHA?

Mostly molecule size, which decides speed and sting. Glycolic acid is smallest and fastest. Lactic acid is bigger, slower, and holds water in the skin. Mandelic acid is bigger again and gentlest of the three. PHAs are larger still, mildest, and the only ones not shown to increase sun sensitivity. None is best; they are a range of speeds.

References

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