Compare · Ingredients

Polyhydroxy Acids vs Urea

Polyhydroxy Acids: Offers exfoliation through ingredients such as gluconolactone and lactobionic acid. Urea: Hydrates dry skin at lower strengths and softens thick scale at higher strengths.

Research updated 2026-10-25

Five PHA toner and serum bottles lined up on white with clear liquid swatches beside them

Five white jars of 40% urea cream lined up, several also listing 2% salicylic acid

Which one?At a glance What it helps Diagrams Using both Strengths Results Safety How it works Products Questions

Which one is right for you?

Choose Polyhydroxy Acids if…

Choose for mild exfoliation when stronger acids are uncomfortable; tolerance still varies.

Sensitive skin that stings with AHAs
Mild dullness or texture
Gentle exfoliation

Choose Urea if…

Choose for dry, rough or thickened skin; match the strength to the body area.

Dry, rough or thickened skin
Cracked heels or keratosis pilaris
Body more than face

Fine together

Can you use both?

Both are gentle on rough skin. Watch for stinging with high-strength urea.

At a glance

● Polyhydroxy Acids

● Urea

Type

Polyhydroxy acid (PHA) family

Humectant and keratolytic

What it does

Offers exfoliation through ingredients such as gluconolactone and lactobionic acid.

Hydrates dry skin at lower strengths and softens thick scale at higher strengths.

Best for

Acne; Dull Skin; Sensitive Skin

Dry Skin; Cracked Heels; Keratosis Pilaris; Eczema

Studied concentrations

14% gluconolactone in an acne trial; newer studies test mixed-acid formulas.

Low-strength moisturizers and higher-strength foot products serve different purposes.

When to use

Start on a few evenings weekly; increase only if comfortable.

Morning or night, as directed by the finished product.

Time to results

Often 8–12 weeks in small cosmetic studies; results may be subtle

Comfort may improve quickly; reassess persistent dryness

Irritation

Can still sting or cause a rash; sensitive skin does not guarantee tolerance.

Can sting cracked, inflamed or sensitive skin; high strengths are unsuitable for routine facial use.

Sensitive skin

Choose a simple formula and test a small area first. Avoid actively inflamed or broken skin unless the product is specifically directed for it.

Choose a simple formula and test a small area first. Individual tolerance matters more than an ingredient’s reputation for being gentle.

Available

Cosmetic or OTC products; some high-strength procedures are separate treatments.

Cosmetic or OTC products; some high-strength procedures are separate treatments.

What it helps

Compare uses by strength of evidence. Evidence level describes confidence in a benefit, not its size.

Evidence level

Polyhydroxy Acids

Urea

Moderate evidenceSome supportive research

—

The front of one shin on pale skin. The surface is pink with fine white flaking and a few shallow cracks, and the skin around it is even in tone.

Dry Skin

Tested urea-containing moisturizers improve dryness and hydration.

Limited evidenceEarly or small studies

Inflamed acne on light skin. The spots sit in a patch of pink, and the ring of redness around each one is easy to see. A few have a yellow-white head, and the skin between them is dry and flaking.

Acne

One controlled trial found fewer lesions with 14% gluconolactone.

Dull Skin on light skin.

Dull Skin

Small studies of PHA formulas suggest smoother surface texture.

Sensitive Skin on light skin.

Sensitive Skin

Some tested formulas were well tolerated; this is not proof that all PHAs suit reactive skin.

Cracked heel on light skin, viewed from the sole with toes pointing upward.

Cracked Heels

Higher-strength products soften thick dry heel skin; painful cracks need assessment.

The back of an upper arm on light skin, covered in small rough bumps at every hair opening. Each bump sits in a faint pink ring, so the arm looks evenly speckled and slightly red.

Keratosis Pilaris

Keratolytic formulas may soften rough bumps; responses vary.

Extreme close-up of light skin in an active eczema flare, too close to tell which part of the body it is. Blotchy pink-red inflammation covers the whole frame with no clear edge, with small raised bumps, fine dry scale and a few fresh scratch marks.

Eczema

May help dry skin between flares but can sting inflamed areas.

Insufficient evidence

The front of one shin on pale skin. The surface is pink with fine white flaking and a few shallow cracks, and the skin around it is even in tone.

Dry Skin

The reviewed sources do not establish this ingredient as a treatment for this concern.

Flat tan patches with soft irregular edges across the forehead and upper cheek of an adult with light skin, the surface completely smooth.

Melasma

The reviewed sources do not establish this ingredient as a treatment for this concern.

Acne scarring on light skin. Small sharply cut pits and broad shallow dips across a cheek, several sitting inside faint flat pink marks, with no active spots.

Acne Scarring

The reviewed sources do not establish this ingredient as a treatment for this concern.

Inflamed acne on light skin. The spots sit in a patch of pink, and the ring of redness around each one is easy to see. A few have a yellow-white head, and the skin between them is dry and flaking.

Acne

The reviewed sources do not establish this ingredient as a treatment for this concern.

AI-generated educational illustration: Thickened yellow great toenail on a light-skinned foot.

Nail Fungus

The reviewed sources do not establish this ingredient as a treatment for this concern.

How it works

Polyhydroxy Acids mechanism diagram. Loosens surface cells: PHAs promote shedding in the outer skin. Helps bind water: Hydroxyl groups contribute to water binding. — Open full-size diagram
Diagram explanation and sources
Loosens surface cells: PHAs promote shedding in the outer skin. Helps bind water: Hydroxyl groups contribute to water binding.
Schematic illustration; not a measurement of skin penetration. Effects vary with ingredient identity and formulation.
Source 1 · Source 2 · Source 3

Urea mechanism diagram. Hydrates the outer skin: Urea acts as a natural water-binding molecule. Softens thickened keratin: Higher strengths have stronger keratolytic effects. — Open full-size diagram
Diagram explanation and sources
Hydrates the outer skin: Urea acts as a natural water-binding molecule. Softens thickened keratin: Higher strengths have stronger keratolytic effects.
Schematic illustration; not a measurement of skin penetration. Effects vary with ingredient identity and formulation.
Source 1

Using both in one routine

Built from where each one usually sits in a routine. Introduce one at a time.

Morning

Step 1

Cleanser

Step 2

Polyhydroxy AcidsMorning or night

Step 3

UreaMorning or night

Step 4

Sunscreen

Night

Step 1

Cleanser

Step 2

Polyhydroxy AcidsMorning or night

Step 3

UreaMorning or night

Strengths and forms

Concentrations

PHA is a family name, not one ingredient or one standard strength. A clinical acne trial used 14% gluconolactone; that result cannot be transferred directly to lactobionic acid or mixed-PHA products.

14%

Studied gluconolactone lotion

An older controlled acne trial tested this specific formula. It does not establish the best percentage for all PHA skincare.

Choosing a strength: Check which PHA is listed, whether the product stays on or washes off, and whether it also contains other exfoliating acids.

Higher strengths: A PHA product can still irritate, particularly when combined with other acids. A high total-acid percentage is not a validated benefit rating.

Formula matters: The individual acid, acidity and base formula matter. A blended-acid percentage does not reveal the amount of each PHA.

Urea’s role changes with concentration: lower strengths mainly moisturize, while stronger formulas soften thick scale. The boundaries overlap rather than switching at one exact percentage.

2–10%

10–30%

30–50%

Moisturizing range

Used in dry-skin moisturizers. Even lower-strength urea may sting cracked or inflamed skin.

Moisturizing and scale-softening range

Used for rough or scaly skin; the area and formula determine whether it is appropriate.

Localized thick-skin treatments

Used for selected calluses, marked thickening or nail problems. Not a general facial moisturizer.

Choosing a strength: Choose for the body area and degree of thickening, not the highest number. Nail treatment and everyday moisturization are different jobs.

Higher strengths: Concentrated products can irritate. People with reduced foot sensation, poor circulation or diabetes should seek advice before treating thick foot skin.

Formula matters: Creams, foams and nail products differ in contact time and intended use. Follow the finished product’s directions.

Forms

Toner · Serum · Cleanser

Lotion · Foot cream · Nail gel

When you’ll see results

Approximate windows, not promises.

● Polyhydroxy Acids

● Urea

First few weeks

First few weeksAssess tolerance and texture; immediate softness can come from the base formula.

First few weeksSkin may feel softer soon after use; relief depends on the formula.

4–8 weeks

4–8 weeksSubtle changes may appear in some tested products; evidence varies.

4–8 weeksJudge hydration, comfort and whether dryness is recurring.

8–12 weeks

8–12 weeksCompare photographs in the same lighting and reassess benefit.

8–12 weeksPersistent cracking, itch or a rash needs reassessment.

3–6 months

3–6 monthsPhotoaging trials often need several months; expect modest rather than dramatic change.

3–6 monthsContinue if comfortable; hydration usually requires ongoing use.

6–12 months

6–12 monthsLong-term evidence is limited for many cosmetic actives; continue only if useful.

6–12 monthsMoisturizing does not establish reversal of structural ageing or scars.

Safety and sensitive skin

Common reactions

Can still sting or cause a rash; sensitive skin does not guarantee tolerance.

Can sting cracked, inflamed or sensitive skin; high strengths are unsuitable for routine facial use.

When to stop

Stop for persistent burning, swelling, blistering or a new rash. Seek urgent care for breathing difficulty or a severe allergic reaction.

Stop for persistent burning, swelling, blistering or a new rash. Seek urgent care for breathing difficulty or a severe allergic reaction.

Sensitive or inflamed skin

Choose a simple formula and test a small area first. Avoid actively inflamed or broken skin unless the product is specifically directed for it.

Choose a simple formula and test a small area first. Individual tolerance matters more than an ingredient’s reputation for being gentle.

Important limits

Do not use a cosmetic product as a substitute for diagnosis of an unexplained, changing or persistent skin problem.

Do not use a cosmetic product as a substitute for diagnosis of an unexplained, changing or persistent skin problem.

Pregnancy

Low-strength leave-on acids are generally considered acceptable; ask the clinician managing your pregnancy.

Very little is absorbed from ordinary strengths on ordinary areas, and urea has a long history of use. Still, check high-strength products over large areas with the doctor managing your pregnancy.

How it works

In the skin

On the skin. The finished product delivers polyhydroxy acids in a particular vehicle.

Entering skin. No single molecular mass. The 500 Da guideline cannot be applied to this whole ingredient family or mixture.

Conversion. No activation step is established as necessary for its intended topical role.

Skin response. PHA ingredients promote surface exfoliation and may also bind water; individual acids and formulas differ.

Additional effects. Proposed pathways do not establish a measured depth of delivery or clinical benefit beyond the studies cited.

On the skin. The finished product delivers urea in a particular vehicle.

Entering skin. Below the 500 Da guideline; delivery still depends on the formula, solubility, stability and skin condition. Size does not prove effectiveness or penetration depth.

Conversion. No activation step is established as necessary for its intended topical role.

Skin response. Binds water in the outer skin; increasing concentration also helps loosen thickened keratin.

Additional effects. Proposed pathways do not establish a measured depth of delivery or clinical benefit beyond the studies cited.

Getting in

No single molecular mass. The 500 Da guideline cannot be applied to this whole ingredient family or mixture.

Below the 500 Da guideline; delivery still depends on the formula, solubility, stability and skin condition. Size does not prove effectiveness or penetration depth.

Product examples

Polyhydroxy Acids

Isntree Hyper Acid 4 AHA BHA PHA LHA 30 Serum
NeoStrata Ultra Moisturizing Face Cream
Gold Bond Ultimate Pedi Smooth Foot Cream

Urea

Naturium Urea 5% Body Serum
Cetaphil Pro Urea 10%

Common questions

Polyhydroxy Acids:What should I choose polyhydroxy acids for?

Choose for mild exfoliation when stronger acids are uncomfortable; tolerance still varies.

Polyhydroxy Acids:How strong is the evidence?

A 150-person trial tested 14% gluconolactone for acne. Evidence from that molecule or a mixed-acid serum does not establish identical effects for all PHAs.

Urea:What should I choose urea for?

Choose for dry, rough or thickened skin; match the strength to the body area.

Urea:How strong is the evidence?

A controlled study of a urea/glycerol cream supports barrier and hydration benefits, but cannot isolate urea. Nail-softening products do not eradicate nail fungus by themselves.

Sources

Sources and further reading

Dermapedia on YouTube