Ingredient

Polyhydroxy Acids (PHAs)

The mildest of the exfoliating acids. They work slowly, hydrate, and suit people who cannot tolerate an AHA.
Dr. Schwarz, MD · Board-certified dermatologistLast reviewed September 8, 2026
Five PHA toner and serum bottles lined up on white with clear liquid swatches beside them

Start here

Polyhydroxy acids are where I send people whose skin has already told them it does not want an acid. They are close relatives of glycolic and lactic acid, but the molecules are bigger and hold more water, so they get in slowly and rarely sting — and they hydrate, which is unusual for an exfoliant. They are not a stronger option in disguise: a PHA does less than a well-tolerated AHA and does it more slowly, but you can use one daily without redness, which is worth a great deal for sensitive or rosacea-prone skin. PHAs also have not been shown to make skin burn more easily, unlike the AHAs, which removes one worry about using an acid year round — sunscreen daily either way.

— Dr. Schwarz, Board Certified Dermatologist

Key Facts

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Also calledPHA, polyhydroxy acid, gluconolactone, lactobionic acid, galactose
TypeSecond-generation hydroxy acid. Exfoliates gently and holds water in the skin.
Strengths soldRoughly 4% to 15% over the counter, depending on which PHA is used
UseMost people can use one daily
Time to work2 to 4 weeks for smoothness, 3 months or more for tone
Prescription neededNo

What It Is

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Polyhydroxy acids are a group, not a single ingredient. The three you will see on labels are gluconolactone, lactobionic acid and galactose. They are related to the alpha hydroxy acids, but each molecule carries several hydroxyl groups instead of one. Those extra groups make the molecule bigger, so it moves into the skin more slowly, and they attract and hold water, so the ingredient behaves partly like a moisturizer. That is why PHAs sit at the mild end of the family. Lactobionic acid also binds metal ions, and both it and gluconolactone show antioxidant activity in the lab. How much that matters on real skin is not established, so treat it as a bonus. They are sold as ordinary cosmetics, usually between 4% and 15%, in serums, moisturizers, toners and cleansers.

How It Works

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A PHA loosens the same protein bonds other hydroxy acids loosen, so dead surface cells let go instead of piling up. The mechanism is not different. The pace is.

Because the molecules are larger and more water-loving, they linger at the surface and cross it slowly. Less acid reaches living skin at any moment, so PHAs sting less, redden less and take longer to show a result.

The second half is hydration. The hydroxyl groups that slow the molecule down also pull water into the surface layer and hold it there, so skin ends up softer rather than tighter — often more noticeable than the exfoliation on dry or sensitive skin.

There is also reasonable evidence that PHAs, unlike AHAs, do not make skin burn more easily. They have been used comfortably in studies on skin prone to rosacea and eczema, and after cosmetic procedures, which is where their reputation for tolerability comes from.

What they do not do is match a stronger acid. For congestion, deep texture change or stubborn pigment, a PHA is the slow road to a smaller result.

Here is where Polyhydroxy Acids (PHAs) acts in the skin, and what the others do instead.

About Polyhydroxy Acids (PHAs)
Compare
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.

PHAs are large, water-loving molecules that barely penetrate at all. They work at the very surface, which is why they rarely sting.

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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No strong evidence for any condition.

Forms

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PHAs are usually built into a moisturizer or cleanser rather than sold as a treatment on their own, which fits how they work — mild enough for a daily product rather than an event. Gluconolactone is the usual main active, lactobionic acid turns up in richer formulas, and galactose is a supporting ingredient. Blended with an AHA or salicylic acid, the PHA softens the experience rather than doing the work.

A row of Polyhydroxy Acids (PHAs) products sold as moisturizer, photographed on white.
Where PHAs belong
Moisturizer
Exfoliation built into the cream you use anyway. The most common form and the easiest to tolerate.
A row of Polyhydroxy Acids (PHAs) products sold as toner, photographed on white.
Daily, low commitment
Toner
Swept on after cleansing. Gentle enough for most people every day.
A row of Polyhydroxy Acids (PHAs) products sold as serum, photographed on white.
Leave-on strength
Serum
Higher concentration in a light base, for skin that needs more than a moisturizer gives.
A row of Polyhydroxy Acids (PHAs) products sold as cleanser, photographed on white.
Reactive skin
Cleanser
On the skin under a minute. The mildest option, and it does the least.
With an AHA or BHA
Combination formula
The PHA takes the edge off a stronger acid. Read which one is at the higher percentage.

Strengths

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The range is narrow and the rungs are closer together than in the AHA family. Frequency matters more than percentage.

WeakestStrongest
Under 4%4% to 8%10% to 15%Professional peel strengths
Supporting role
Under 4%
Added to cleansers and moisturizers for mild smoothing. Not a treatment strength.
Everyday
4% to 8%
Comfortable daily on most skin, including sensitive skin. Where most PHA products sit.
The upper end
10% to 15%
About as strong as PHAs get at home, roughly a low-strength AHA. Still tolerated daily by many people.
In clinic
Professional peel strengths
Less common than other peels, applied and timed by a trained person.

Basics

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When to Apply
Morning or night, after cleansing, before or as your moisturizer depending on the product. No need to keep it away from other steps.
How to Start
Once a day suits most people, which is unusual in this family. Very reactive skin can start every other day for a week.
If It Irritates
Uncommon, but possible on a damaged barrier. Drop to a few times a week or a lower percentage. If a PHA stings, the problem is usually the state of the skin, not the product.
If It’s Not Working
Give it twelve weeks before judging it on tone. If texture and dullness improved but pigment did not, you need a stronger ingredient, not more of this one — mandelic or lactic acid next.

Sample Routine

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Here is where Polyhydroxy Acids (PHAs) 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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Days 1 to 7Weeks 2 to 4Weeks 6 to 12After 12 weeks
Adjusting
Days 1 to 7
Usually nothing — little or no stinging, and skin feels softer straight away.
Working
Weeks 2 to 4
Skin feels smoother, looks less dull. Visible flaking is unusual.
Building
Weeks 6 to 12
Tone evens out slowly — this part takes patience.
Judge it here
After 12 weeks
If daily use changed texture but not tone, that is the ingredient's ceiling, not your routine.

What to Avoid

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  • Very few conflicts PHAs fit into almost any routine.
  • Using one on top of another acid An AHA or salicylic acid every day removes the reason you chose a PHA.
  • Scrubs, brushes and rough cloths Gentle chemical exfoliation plus physical scrubbing is still too much.
  • Expecting it to replace a treatment Acne, melasma and sun damage need more than a supporting player.
  • Skipping moisturizer On the grounds that the PHA hydrates. It draws water in. Something has to hold it there.
  • Skipping sunscreen PHAs do not appear to increase burning, but sun causes most of the tone problems people buy them for.
  • Applying to broken or freshly treated skin Wait until the barrier is intact.

If You Stop

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Softness and smoothness fade over a few weeks as the surface layer builds up again. Because much of what a PHA does is hydration, the change can feel quicker than with a stronger acid, even though less has been undone. Any pigment that faded stays faded. The cells holding it have been shed, not switched off. There is no rebound; skin returns to its own baseline. PHAs are designed for long-term daily use, and staying on one indefinitely is normal.

Ask Your Doctor

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If you are pregnant or breastfeeding
Ask the doctor managing your pregnancy first.
If your skin is stinging on a PHA
That usually means a damaged barrier — worth a look rather than pushing on.
If you have rosacea or eczema
And are not sure where to start. A PHA often suits, but confirm it fits your plan.
If you have melasma or dark marks
Both need a proper plan; a mild exfoliant is rarely enough.
If new dark or pale patches appear
On treated skin, especially on deeper skin tones.
If you use prescriptions on the same area
Ask where a daily exfoliant fits.
If redness or swelling appears
And does not settle within a day, stop and have it checked.

How It Compares

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Four glycolic acid toner and liquid bottles lined up on white, one with its box16:9 hero for Glycolic Acid. Never cropped: the tone strip and the corner logo depend on the full frame.

Glycolic acid

Better

Considerably faster and better studied, and much more likely to sting and to increase sun sensitivity.

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

Better

Also hydrating and reasonably gentle, but stronger and faster than a PHA, and it does increase sun sensitivity.

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

Better

The gentle end of the AHA family, and the natural step up from a PHA when you want more effect.

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

Gets inside the pore, which a PHA does not, so it is the better choice for blackheads and acne.

Five azelaic acid tubes and bottles on white, most marked 10 percent, from Peach Slices, Paula's Choice, Facetheory, The Ordinary and NaturiumLabeled cutaway diagram of a single skin pore, headed Azelaic 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. Three callout lines point in: decreases dead cells in pore and kills bacteria are drawn in dark navy as main effects, and decreases inflammation is drawn in gray as a lesser one.

Azelaic acid

Different job

Gentle and suitable for rosacea, and it treats acne and dark marks rather than exfoliating.

Six niacinamide products on white, including The Ordinary 10% + Zinc 1%, Paula's Choice Booster and EltaMD UV ClearLabeled cutaway diagram of a single skin pore, headed Niacinamide. 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. Two callout lines point in: decreases inflammation is drawn in dark navy as the main effect, and decreases oil production is drawn in gray as a lesser one. Nothing points at the dead cells blocking the pore.

Niacinamide

Different job

Not an exfoliant at all, but a common companion for sensitive skin working on tone and barrier at the same time.

Plain moisturizer

Different job

For comfort, none for exfoliation. If comfort is all you need, a PHA is not required.

Myths

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  • “PHAs are just weak AHAs.” They are chemically different, not diluted. The extra hydroxyl groups change the molecule's size and water-loving behavior — hence slower, and hydrating.
  • “Because they are gentle, they do nothing.” They exfoliate, more slowly and to a smaller degree. For skin that reacts to everything, usable beats effective in theory.
  • “PHAs mean I never need sunscreen.” Not being shown to increase burning is not protection. Daily sunscreen is still the most useful step for tone.
  • “They are only for sensitive skin.” That is where they help most, but any skin type can use one daily.
  • “A PHA will clear my acne or fade my melasma.” They contribute at the edges. Both need dedicated treatment.
  • “Gentle means I can use as much as I want.” Daily use is fine. Stacking three products that all contain one is still overdoing it.

Questions Patients Ask

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What actually makes a PHA different from an AHA?

The molecule is bigger and carries more water-attracting groups, which slows its entry, so it stings less, and makes it hold water as well as exfoliate. The exfoliation itself is the same.

Do PHAs make my skin more sensitive to the sun?

They have not been shown to, a genuine difference from the AHAs. That is not protection, and daily sunscreen remains the most useful thing for tone.

Can I use one every day?

Most people can, and that is the usual way they are used. If your skin is very reactive, start every other day for a week.

Are they strong enough to be worth it?

For rough texture, dullness and dryness, yes. For active acne, melasma or significant sun damage, they support the treatment rather than being it. If you tolerate stronger acids, a PHA may be slower than you need.

Which PHA should I look for?

Gluconolactone is the most common main active. Lactobionic acid sits in richer products, galactose is usually a supporting ingredient. The formula and percentage matter more than which of the three is on the label.

Can I use a PHA with a retinoid?

Usually yes, and it is a comfortable pairing — part of why PHAs get recommended to people starting a retinoid. While your skin is still adjusting, keep the routine simple.

References

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