Lactic Acid

What Is Lactic Acid in Skincare?

Lactic acid is an alpha hydroxy acid (AHA) best known as the natural acid in soured milk and yogurt. In skincare it does two jobs at once: it gently loosens dead surface cells so skin looks smoother and brighter, and it acts as a humectant that helps the surface hold water. Its larger molecule makes it a gentler choice than glycolic acid for dry or easily stressed skin.

EWG Skin Deep rating for Lactic Acid

Lactic Acid Quick Facts

How Lactic Acid Works on the Skin

Like all AHAs, lactic acid weakens the bonds between dead cells on the skin's surface, so they shed evenly instead of building up into a dull, rough layer. Because its molecule is larger than glycolic acid's, it moves into the skin more slowly, which is why many people find it gentler. Lactic acid is also part of the skin's own natural moisturizing factor (NMF), the mix of water-binding compounds in the outer layer, so it adds a hydrating effect that glycolic acid does not.

How strong a lactic acid product is depends on both its percentage and its pH. In a randomized, double-blind, placebo-controlled study, Thueson and colleagues (1998) tested lactic acid on 26 adult women: 10% lactic acid at pH 2.0, 3.0, and 4.0, and 5%, 10%, and 15% lactic acid at pH 3.0. They measured how fast the surface layer renewed using a dansyl chloride stain. At the same concentration, the exfoliating effect depended strongly on pH; at the same pH, it depended on concentration. The authors concluded that the free acid in the formula is what does the work. This is why two "10% lactic acid" products can feel completely different.

AHAs, including lactic acid, also increase sensitivity to the sun. The FDA recommends that AHA products carry a sunburn alert and that users wear sunscreen during use and for a week afterward.

How to Use Lactic Acid

• Start with a lactic acid cleanser or a low-strength leave-on two or three times a week, in the evening.
• Apply to clean, dry skin and follow with a moisturizer.
• Wear broad-spectrum sunscreen every morning, and keep wearing it for a week after you stop.
• Alternate with retinol rather than layering both in one application.

Formulating Notes

• Add lactic acid to the water phase, at cool-down for emulsions (below 40°C / 104°F), then measure and adjust the final pH with a calibrated meter.
• For a leave-on exfoliating product, target a final pH of 3.5-4.0 and no more than 10% lactic acid. Adding a little sodium lactate raises the pH and buffers the formula so it feels gentler.
• For simple pH adjustment, a few drops of an 88% solution are often enough; add drop by drop and re-measure.
• Choose acid-tolerant thickeners (xanthan gum, hydroxyethylcellulose) and a preservative that works at low pH.

Who Lactic Acid Suits

Lactic acid is a strong fit for dry, mature, and dull-looking skin, and for anyone who finds glycolic acid too intense. If you have sensitive skin, patch test first (inner arm, 24 hours) and start at the lowest rate in the range, then work up. Modern cosmetic lactic acid is made by fermentation and contains no milk protein or lactose, so a lactose intolerance is not a reason to avoid it.

Frequently Asked Questions

What does lactic acid do for skin?

Lactic acid gently loosens dead surface cells so skin looks smoother and brighter, and it helps the surface hold water. It is one of the gentlest alpha hydroxy acids.

Is lactic acid better than glycolic acid?

Not better, different. Glycolic acid is smaller and works faster; lactic acid is gentler and adds hydration. Dry and sensitive skin usually prefers lactic acid.

Can I use lactic acid every day?

Many people can once their skin is used to it, especially in a cleanser. Begin a few times a week and increase only if your skin stays comfortable.

What percentage of lactic acid should I use?

Retail leave-on products are limited to 10% or less at a pH of 3.5 or higher under the CIR safety conclusion. pH matters as much as percentage, so a 5% product at a low pH can feel stronger than a 10% product at a higher pH.

Can I use lactic acid with retinol or niacinamide?

Niacinamide pairs well with lactic acid. Alternate lactic acid and retinol on different nights rather than layering them.

Is lactic acid good for sensitive skin?

It is often the first AHA recommended for sensitive skin. Patch test on the inner arm for 24 hours and start with a low strength a few times a week.

Is lactic acid made from milk?

Lactic acid was first found in soured milk. Cosmetic lactic acid is made by fermenting plant sugars and contains no lactose or milk protein.

What does chirally correct lactic acid mean?

Lactic acid exists in two mirror-image forms, L and D. The L-form is the one the skin itself makes. Learn more on our chirally correct skincare page.

Shop Lactic Acid Products

Our Alpha Hydroxy Probiotic Cleanser Chirally Correct combines lactic and salicylic acids with yogurt extract in a light gel cleanser for a brighter-looking complexion. For serum tips and a deeper guide, read What Is Lactic Acid Serum?, or compare it with mandelic acid in Lactic Acid Exfoliator vs Mandelic.

Sources

• Thueson DO, Chan EK, Oechsli LM, Hahn GS. The roles of pH and concentration in lactic acid-induced stimulation of epidermal turnover. Dermatol Surg. 1998;24(6):641-645. doi:10.1111/j.1524-4725.1998.tb04221.x
• U.S. Food and Drug Administration. Alpha Hydroxy Acids (CIR safety conclusions for glycolic and lactic acid; sunburn alert).

These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.

About the Author
Written by Kari Thomas, cosmetic formulator and founder of Skin Perfection.