Dermatologist's Take
Lactic acid is an alpha hydroxy acid (AHA) that does two jobs at once: it loosens dead surface cells so they shed, and it holds water in the skin because your skin already uses lactate as one of its own moisturisers. That double action is what separates it from glycolic acid. Its strongest evidence is for dry, scaly and rough skin — 12% lactate lotion clearly beat plain moisturiser in double-blind trials from the 1980s, and it is the topical most dermatologists reach for first in keratosis pilaris. The anti-aging evidence is thinner and older, and the one trial that pitted a lactic acid peel against a glycolic acid peel for melasma favoured glycolic. Two practical points matter more than the percentage on the front: the pH decides how much of it is active, and it makes skin temporarily more sun-sensitive, so sunscreen is not optional.
At a glance
- AKA 2-hydroxypropanoic acid, L-lactic acid, ammonium lactate (the neutralised form)
- 5–12% for leave-on products; 12% ammonium lactate for body; 80–90% for in-office peels
- Works with niacinamide, ceramides, urea, moisturizers. Space it out from retinoids
- Evidence: Strong for dry and scaly skin · Moderate for texture and rough bumps · Limited for wrinkles
What is it?
Lactic acid is an alpha hydroxy acid, or AHA — the same family as glycolic acid. It occurs naturally in milk and fermented foods, which is where the name comes from, but the lactic acid in skincare is made in a lab.
It shows up in three quite different kinds of product, and they are not interchangeable:
- Leave-on serums, lotions and creams, usually 5% to 12%. These exfoliate.
- Ammonium lactate 12% — lactic acid that has been neutralised into a salt. Sold for dry, scaly body skin. In the US, one version (Lac-Hydrin) is prescription and another (AmLactin) is sold over the counter.
- In-office peels, at 80% to 90%. These are applied by a clinician and rinsed off.
Your skin also makes lactate on its own. It is one of the compounds in what dermatologists call natural moisturising factor — the mix of small water-binding molecules sitting in the outer layer that keeps skin from drying out. Lactic acid is unusual among the exfoliating acids in being something the skin already uses.
How it works
Two things happen, and they pull in different directions.
It loosens the glue between dead cells. The outer layer of skin is held together by protein rivets called desmosomes. AHAs weaken those rivets in the very top layers, so dead cells release and shed instead of piling up. That is what smooths rough texture and softens scale. A caveat worth stating: the detailed microscope study that established this was done with glycolic acid, and the finding is extended to lactic acid rather than proved for it directly.
It holds water. Lactate is one of the skin's own moisturisers. Studies of people with mild eczema show lactate levels in the outer skin run low, and putting it back raises skin hydration. Lactic acid also appears to prompt skin cells to make more ceramides — the barrier fats — which is a second, slower route to the same result.
That combination is genuinely unusual. Most exfoliating acids only strip. Lactic acid strips and hydrates, which is a large part of why it suits dry and scaly skin better than glycolic acid does.
Subtypes
Three names on labels cause most of the confusion.
- Lactic acid — the free acid. This is the exfoliating form. How much of it is actually active depends on pH, not just percentage.
- Ammonium lactate — lactic acid neutralised with ammonia to make a salt. Ammonium lactate 12% lotion sits at around pH 4.5 to 5.5, which means most of it is not in the active acid form. That is deliberate. It makes the product mild enough to use daily on large areas of the body, and it is a moisturiser for dry, scaly skin rather than a facial exfoliant. A 12% ammonium lactate lotion and a 12% lactic acid serum are very different products.
- L-lactic acid versus DL-lactic acid — lactic acid comes in two mirror-image forms. Most cosmetic lactic acid is a mix of both unless the label says otherwise. Two studies from 1996 found the L form raised skin ceramides more and stung less than the D form. Both were run by cosmetic company scientists and neither has been repeated in patients, so treat this as an interesting formulation preference rather than a proven advantage.
Concentrations
The number on the front of the bottle only tells you half the story. The other half is pH, because only the un-neutralised acid exfoliates. At pH 3.5, roughly 70% of the lactic acid is in the active form. At pH 5.0, it is about 7%. Same percentage, very different product.
- 5% — in one study, this improved the surface and outer layer of skin but produced no change deeper down.
- 12% leave-on — the strength where that same study saw thickening in the deeper layer. This is also the strength used in the dry-skin trials.
- 10% is the ceiling for US consumer products, at pH 3.5 or higher, under the industry safety panel's guidance. The EU is far stricter: 2.5% at pH 5.0 or above for products sold to the public — which is why an EU lactic acid product may behave quite differently from a US one with the same label.
- Up to 30% is sanctioned for salon use with rinsing, by trained staff.
- 80% to 90% appears in published dermatology peel protocols, applied by a clinician. This is not a home product.
Conditions it treats
What to expect
For rough, bumpy or scaly skin, expect gradual smoothing over two to four weeks of daily use. The dry-skin trials ran three weeks and measured a real advantage over plain moisturiser that persisted for two weeks after stopping.
Stinging is the characteristic side effect, and it tracks how damaged the skin already is. On the prescription 12% ammonium lactate label, stinging and burning were each reported by about 1 in 30 people with ordinary dry skin — and by about 1 in 10 people with ichthyosis, where the barrier is far more compromised. If it stings badly, that is usually a sign the skin underneath is more irritated than you thought.
Sun sensitivity is real and worth taking seriously. AHAs temporarily make skin more prone to UV redness and UV damage. The US FDA recommends using sunscreen while you use an AHA product and for a week after stopping. The good news is that the effect is fully reversible — it was gone a week after people stopped. The underlying research was done with glycolic acid rather than lactic acid, and the warning applies to the whole AHA family.
Benefits stop when you stop. In keratosis pilaris in particular, more than 60% of dermatologists surveyed reported their patients relapsing within three months of stopping topical treatment.
The evidence4 studies
Studies behind the treatments above. Tap any tag to see what it means.
L-lactic acid 8% cream improved facial photodamage by at least one grade in 71% of users over 22 weeks, against 40% on the cream base alone.
Strong evidence
Randomised, double-blind and vehicle-controlled — meaning the comparison was against an identical cream without the acid, so the result is not just the moisturiser working. Run at a hospital rather than by a manufacturer. 74 people is modest but adequate for the endpoint.
74 people
How many people took part. Bigger studies are less likely to show a result by chance alone.
Modest effect
The authors' own word for the result was "modestly useful." A 71% versus 40% response rate on a nine-point photodamage scale means many people moved by one grade, not that skin was transformed.
12% lactate lotion reduced dry, scaly skin more than both plain moisturiser and 5% lactic acid, and the advantage was still there two weeks after stopping.
Strong evidence
Randomised, double-blind, and compared on opposite sides of the same person, which removes most of the differences between individuals. The follow-up period after treatment stopped is what makes it unusually informative.
60 people
How many people took part. Bigger studies are less likely to show a result by chance alone.
An 80% lactic acid peel lowered melasma scores less than a 50% glycolic acid peel over four sessions, with no difference in side effects.
Moderate evidence
Randomised with an active comparator, which is the right design for this question. Graded moderate rather than strong because 40 people is small, only the participants were blinded, and six were lost to follow-up.
40 people
How many people took part. Bigger studies are less likely to show a result by chance alone.
Lactic acid 10% cream reduced keratosis pilaris bumps by 66% over three months, compared with 52% for 5% salicylic acid.
Limited evidence
Randomised against an active comparator, but with no placebo or plain-moisturiser arm — so it cannot separate what the acid did from what any cream would have done in a condition that responds to moisturising. Graded limited for that reason, not because the result is implausible.
No placebo group
Both groups got an active cream. Without an untreated or vehicle-only comparison, part of the 66% is likely the effect of applying a moisturiser twice daily for three months.