Dermatologist's Take
Urea is a small molecule your skin already makes and keeps in its outer layer to hold water. Added back in a cream, it does two different jobs depending on how much is in there: low strengths mainly hydrate, high strengths dissolve thickened keratin. Its best evidence is for genuinely scaly, thickened skin — ichthyosis, cracked heels, and 40% urea to soften and lift a fungal nail — and for keeping eczema in remission, where a 5% urea cream cut the risk of flare-up by 37% in a proper double-blind trial. Where it is weaker than its reputation: against a plain moisturiser on ordinary dry skin, the one trial that compared urea with its own identical base found no advantage on the arms, only on the more scaly legs. Where you see "10% is where urea switches from moisturiser to exfoliant," treat that as a rule of thumb rather than a measured fact — expert reviews put the line anywhere from 10% to 20%.
At a glance
- AKA carbamide. One of the skin's own water-binding compounds
- 2–10% hydrates · 10–30% does both · 30–50% dissolves thick keratin and softens nails
- Works with ceramides, glycerin, lactic acid, topical steroids and antifungals
- Evidence: Strong for ichthyosis and nail softening · Moderate for dry skin and eczema · Thin for keratosis pilaris
What is it?
Urea is a small, simple molecule — your body makes it constantly as a waste product of digesting protein. It is also a normal part of your skin. The outer layer holds a mix of small water-binding compounds that dermatologists call natural moisturising factor, and urea is one of them.
No, it is not harvested from urine. Urea was first isolated from urine in the 1700s, which is where the name and the squeamishness come from. The urea in skincare and in medical creams is made industrially from ammonia and carbon dioxide. It is the same molecule, purified to pharmaceutical grade. Nothing is collected from anything.
You will find it across a wide range of strengths, from 2% in a face moisturiser to 40% in a foot cream or a nail preparation. That range is not just marketing. Urea genuinely does different things at different concentrations, which is why it is worth understanding before you buy.
How it works
Urea works three ways, and they layer on top of each other as the concentration rises.
It holds water. Urea is hygroscopic — it grabs water and keeps it in the outer layer of skin, which reduces the amount evaporating away.
It changes what skin cells do. This is the genuinely interesting part, and it is better established than most ingredient claims. Urea does not just sit on the surface. It is actively carried into skin cells by dedicated transporters, and once inside it turns up production of filaggrin, loricrin and the enzymes that build the skin's barrier fats — plus the skin's own antimicrobial peptides. Blocking the transporters blocks the effect. That was shown in a human study, not a test tube.
At high strength, it dissolves keratin. Urea breaks the hydrogen bonds holding keratin proteins in shape. At 40% or so, in the concentrations used for nails and calluses, this is essentially controlled protein denaturation — which is also why it softens a nail plate enough to lift it away.
The same property makes urea a penetration enhancer: it opens up thickened, keratin-dense tissue so that other drugs — antifungals, steroids, psoriasis treatments — can get through.
Subtypes
Concentrations
This is the part worth reading before you buy anything.
- 2–10% — mainly a moisturiser. Used in face and body creams, in eczema-prone skin, and in ichthyosis. 10% is the most common single strength.
- 10–30% — does both jobs. Hydrates and starts softening thickened skin. This band suits rough texture, elbows, knees and shins.
- 30–50% — mainly keratin-dissolving. Used for calluses, corns, thickened heels, hyperkeratotic patches, and for softening a diseased nail so it can be removed. Not a face product.
About the "10% is the switch" rule. You will see this stated everywhere as fact. It is not one. Different expert reviews put the change-over at 10%, at 15%, or at 15 to 20%, and no dose-ranging trial has ever established a threshold. Mechanically, the transition is a gradient rather than a switch — a 40% cream is chemically strong enough to denature protein in a way a 10% cream simply is not. Treat "roughly 10 to 20%" as the transition zone and the exact number as convention.
More is not automatically better in the moisturising range. One study found no difference between 5% and 10% urea in eczema. Higher percentages below the keratolytic range mostly buy irritation rather than results.
Conditions it treats
What to expect
For dry or scaly skin, expect improvement within days to two weeks with twice-daily use. For thickened heels or calluses at 30% and above, allow a few weeks of consistent use.
Stinging is the main complaint, and it is predictable. Urea stings most where the skin is already broken — cracked heels, eczema fissures, eroded patches. Intact skin has a layer of dead cells for the urea to act on; broken skin does not, so it reaches living tissue directly. In one 197-person eczema trial, about a quarter of people using a urea-and-saline cream rated smarting as moderate or severe, against one in ten on a glycerin cream. Manufacturer labels for 40% urea say the same thing: transient stinging, burning or itching that settles when you stop.
The standard advice is to keep urea off broken, weeping, infected or angrily red skin, and off the eyes.
A urea cream can smell faintly of ammonia. That is not spoilage in the usual sense — urea slowly breaks down in water into ammonia and carbon dioxide. Well-made products buffer against this. A tube that smells strongly is probably old and probably weaker than the label says.
Allergy to urea itself is essentially unreported. One caution: imidazolidinyl urea and diazolidinyl urea are completely different chemicals — they are preservatives, and they are recognised allergens. Sharing part of a name is all they share.
The evidence4 studies
Studies behind the treatments above. Tap any tag to see what it means.
A 5% urea cream cut the risk of eczema flaring back up by 37%, and at six months 26% of users were still clear against 10% on the comparison cream.
Strong evidence
Randomised, double-blind, multicentre, with a pre-specified relapse endpoint. This is the design that answers the question properly. Note the first author works for the cream's manufacturer, which is disclosed.
Relapse prevention
Everyone entered the study with their eczema already under control. The question was not whether the cream treats eczema, but whether it delays the next flare.
Maker-funded
Paid for by the company that sells the product. That doesn't make the result wrong, but independent studies reaching the same conclusion would be more convincing.
A 7.5% urea cream beat its own identical base on the legs, where scaling was heaviest, but showed no advantage on the arms.
Moderate evidence
The only study of urea in ichthyosis that compared it against a truly identical cream without the urea — the design that separates the ingredient from the moisturiser. Graded moderate rather than strong only because 14 people is very few.
14 people
How many people took part. Bigger studies are less likely to show a result by chance alone.
Worked only where skin was worst
On the arms, urea and the plain base performed the same. The urea advantage appeared only on the legs, where the skin was more thickened and scaly — which is the study's most useful finding.
A 40% urea ointment under a plastic dressing removed the infected nail plate in 61% of people within three weeks, against 39% for a urea-plus-antifungal ointment.
Strong evidence
Randomised, multicentre, with the assessors blinded to which treatment each person had. It hit its main endpoint. This is the best evidence for high-strength urea.
105 people
How many people took part. Bigger studies are less likely to show a result by chance alone.
Removes the nail, not the fungus
The endpoint was clearing the diseased nail plate — a mechanical result. Both groups then needed an antifungal cream to treat the infection itself.
Topical urea is carried into skin cells by dedicated transporters, where it switches on the genes that build the barrier and the skin's own antimicrobial peptides.
Moderate evidence
A mechanistic human study rather than a treatment trial, so it cannot tell you how well urea works in practice. It is graded moderate because it included transporter-blocking controls, which is what makes the finding convincing rather than merely suggestive.
21 people
How many people took part. Bigger studies are less likely to show a result by chance alone.