What Is Lactic Acid? Benefits & How It Works

What is Lactic Acid?

Lactic Acid is an alpha hydroxy acid (AHA), a type of exfoliating acid. It was first found in sour milk, which is where the name comes from, but the lactic acid used in skincare is usually made by fermenting sugars rather than taken from milk. It is also a natural part of healthy skin, where its salt, sodium lactate, helps hold water in the outer layer.

Lactic acid is often described as one of the gentler AHAs. It exfoliates the skin surface and also hydrates, which is why it is popular for dry, dull or rough skin and for people who find glycolic acid too harsh.

Source

Found in	Lactic Acid (INCI name); its salt is Sodium Lactate
Origin	Naturally in sour milk and in skin; cosmetic grade is usually made by fermentation of sugars
Also known as	AHA, alpha hydroxy acid, milk acid

Top features and benefits

Gently exfoliates dead skin cells	Helps smooth rough, dull skin	Attracts water and supports hydration
Part of the skin's natural moisturizing factors (as sodium lactate)	May help improve the look of sun-damaged skin over months	May support the look of an even skin tone
Often gentler than glycolic acid	Available in cleansers, serums and body products	Works at a range of strengths

How Does It Work?

Lactic acid works by loosening the glue that holds dead skin cells together on the surface. Once that glue is loosened, the dull outer cells shed more easily, which reveals fresher-looking skin underneath. With regular use, skin can feel smoother and look brighter.

Two things decide how strong the effect is: the concentration and the pH of the product. Lactic acid needs to be in its free acid form to work, and that happens at a lower pH. A controlled trial found that both the pH and the concentration matter. Paula's Choice describes exfoliation as best at a pH of about 3 to 4 and a concentration of about 5 to 12 percent. A low-strength lactic acid in a higher-pH product may mainly act as a moisturizer.

Lactic acid also differs from some other AHAs because it helps hydrate the skin as well. Its molecule is larger than glycolic acid's, so it is generally considered gentler. Over longer periods, studies have linked lactic acid at around 8 percent to improvement in sun-damaged skin after several months. As with all AHAs, skin becomes more sensitive to the sun, so daily sunscreen is important.

Frequently Asked Questions

What does lactic acid do for skin?

Lactic acid gently exfoliates the surface of the skin and also helps it hold onto water. This can make rough, dull skin feel smoother and look brighter.

Is lactic acid gentler than glycolic acid?

Generally yes. Lactic acid is a larger molecule than glycolic acid and tends to be less irritating at similar strengths, though the product's pH and concentration matter most.

How does lactic acid compare with glycolic and mandelic acid?

Glycolic acid is the smallest AHA and usually the strongest. Mandelic acid is larger and slower acting, so it is often gentler. Lactic acid sits in between, with added hydration. See the Glycolic Acid and Mandelic Acid pages for more.

What percentage of lactic acid is best?

It depends on the goal and skin. Lower strengths mostly hydrate and lightly exfoliate, while exfoliation is usually associated with about 5 to 12 percent at a low pH. Beginners usually do best starting at the low end.

How often can I use lactic acid?

Start with once or twice a week and build up as your skin tolerates it. If you feel stinging, redness or dryness, cut back.

Can lactic acid be used with niacinamide, retinol or vitamin C?

Lactic acid is often used with niacinamide. Using it with retinol or vitamin C in the same routine can raise irritation risk, so many people use them at different times or on alternate days.

Does lactic acid make skin sensitive to the sun?

Yes. Exfoliating acids can make skin more sensitive to sunlight, so use sunscreen daily while using lactic acid.

Is lactic acid safe for sensitive skin?

Lower strengths can be tolerated by many sensitive skin types, but irritation is possible. Patch test and introduce slowly.

Is lactic acid safe in pregnancy?

Many sources consider low-strength topical AHAs acceptable, but you should check with your doctor before using any active ingredient while pregnant.

Is lactic acid made from milk? Is it vegan?

The name comes from milk, but cosmetic lactic acid is usually produced by fermenting sugars and is often vegan. Check the brand's sourcing if it matters to you.