Lactic acid

Acid5–10%

A gentler alpha hydroxy acid that smooths and brightens while also helping skin hold on to moisture.

What it is

Lactic acid is an alpha hydroxy acid (AHA) made by fermenting sugars, and part of the skin's own natural moisturising factor. It lifts away dull surface build-up for smoother, brighter-looking skin, and usually feels gentler than glycolic acid.

Good for

Dull skinRough textureDry skinUneven toneFine lines

How it works

Lactic acid weakens the bonds between dead surface cells so they shed evenly. It is generally reported to sting less than glycolic acid, although skin absorption tests show the two penetrate to a similar extent. It also attracts water, and in studies it improved smoothness and the look of fine lines.

Ratings

Evidence

4/5

Controlled studies show smoother skin and better hydration.

Gentleness

3/5

Usually milder than glycolic acid but increases sun sensitivity.

Formulation difficulty

2/5

Water-soluble, but needs pH control and acid-resistant packaging.

Cost

1/5

Inexpensive commodity raw material.

Popularity

4/5

Steady demand and common in gentle exfoliating launches.

Pairs and cautions

Pairs well with

In a routine. Pairing in one formula depends on matching pH windows.

Take care with

Retinoids or other strong acids in the same stepAdds irritation
Very sensitive or compromised skinCan sting
Exfoliating products for babies and young childrenNot suited to young skin
Use straight after shaving or waxingLikely to sting

Formulations it suits

Toner, essence and face mist Serum Gel and foaming cleanser Lotion Cream Cream or sleeping mask Body wash Hand cream

Packaging

Regional considerations

Australia	Not scheduled in the Poisons Standard, unlike glycolic acid, so Australia sets no strength or pH limit for cosmetic use.
United States	No legal limit, but the CIR panel supports 10% or less at pH 3.5 or above for consumer use, and FDA recommends a 'Sunburn Alert' on AHA labels.
ASEAN	Treated like glycolic acid: up to 10% at pH 3.5 or above for general use, 20% at pH 3.0 or above for professional use, and a sunburn alert at 2.5% or more without sunscreen.
Climate	AHAs leave skin more prone to sunburn for about a week after use, which matters in high-UV markets such as Australia, so add daily sunscreen directions to the pack.

In the lab

Specifications

Typical use level

5–10%0525%

pH window

pH 3.5–62 acid7 neutral10 alkaline

Solubility

Water-soluble

Sensitive to

High pH

5–10% at pH 3.5–4 for exfoliating serums; moisturisers use 1–5% at a higher pH, where it acts mainly as a humectant.

INCI	Lactic Acid
Also known as	AHA, Alpha hydroxy acid, L-lactic acid, Sodium lactate (salt form)
Origin	biotech/fermentation

Lab notes

Solubility and phase

Water phase. Supplied as an 80–90% solution, so adjust the dose for active content.

Stability

Set strength through pH and the free-acid fraction, and check emulsion and thickener stability at low pH.

Regulatory, Australia

Lactic acid, including the L-form, and sodium lactate are on the AIIC. It is not scheduled in the Poisons Standard, unlike glycolic acid, and has no EU limit.

Claims to take care with

'Exfoliates', 'smoother, brighter-looking skin' and 'hydrates' are cosmetic. Include sun-protection advice and avoid wording that implies a medical procedure.