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Skin Actives

Lactic Acid

Also known as: L-lactic acid, Alpha-hydroxypropanoic acid, Milk acid

The gentlest AHA — the skin's own exfoliant and humectant, ideal for sensitive-skin resurfacing and hydration.

  • By IngredientWiki Editorial Team
  • Fact-checked by IngredientWiki Editorial Team
  • Updated 2026-09-26
  • 2 min read

In short

Lactic acid is an alpha-hydroxy acid (AHA) produced naturally by the body and famously by milk fermentation — hence its name. In skincare it does two jobs at once: it dissolves the bonds holding dead surface cells, exfoliating gently, and it acts as a humectant, drawing water into the skin — the reason it is considered the most hydrating and best-tolerated AHA. Clinical trials document improved skin texture, hyperpigmentation, and hydration with concentrations from 5% (cosmetic) to 40–70% (professional peels). Its larger molecular size makes it penetrate more slowly than glycolic acid, trading raw power for comfort — which is exactly its niche.

  • AHA produced endogenously; 'milk acid' historically
  • Exfoliates and hydrates simultaneously
  • Gentlest major AHA — larger molecule, slower penetration
  • 5–10% daily use; 40–70% professional peels

What is Lactic Acid?

Lactic acid is the AHA your skin already knows — the body manufactures it, and milk's souring tradition gave it a name before chemistry gave it a structure. As a skincare acid it has a two-for-one profile: gentle exfoliation of dead surface cells plus humectant hydration in the same molecule. That combination makes it the entry point of the acid world — effective enough for texture, pigment, and mild acne concerns, forgiving enough for sensitive skin and first-time acid users who would flake out on glycolic.

Where it comes from

Natural sources

  • Endogenous to human skin as part of the natural moisturizing factor
  • Historically derived from soured milk (Cleopatra's milk-bath tradition)
  • Modern commercial production by sugar fermentation

How it's made

Cosmetic concentrations 5–10% daily; professional peels 30–70%.

What it does in products

  • Corneocyte desmosome dissolution (exfoliation)
  • Humectant water binding
  • Ceramide synthesis stimulation
  • Pigmentation and texture improvement

Benefits

Gentle exfoliation and texture

strong evidence

Trials show improved smoothness, fine lines, and skin tone with daily 5–10% use and deeper resurfacing with peels.

Hydration support

strong evidence

Increases natural moisturizing factor and ceramide production — a moisturizing bonus no other major AHA matches.

Hyperpigmentation and acne support

moderate evidence

Clinical studies document fading of photodamage pigment and reduced acne lesions, comparable in direction to other AHAs at matched strength.

Side effects & safety

Mild stinging and redness at initiation (uncommon)Less than glycolic acid; usually transient.
Sun sensitivity (common)Standard AHA caution — daily SPF required.

Safety considerations

  • Cosmetic concentrations (≤10%) generally considered acceptable in pregnancy; professional peels are avoided.
  • Other exfoliants — additive irritation; don't stack in one routine
  • Retinoids — alternate nights to manage irritation
  • Not for: None; patch-test if highly reactive

How it's used

In supplements

Not an oral skincare ingredient (dietary lactic acid is a fermentation byproduct, unrelated).

In skincare

5–10% serums and lotions 2–3 nights weekly; 30–70% professional peels in clinic.

Regulatory status

  • Cosmetic ingredient at ≤10% (pH ≥3.5); higher concentrations are professional-use. GRAS as a food ingredient.
  • GRAS (generally recognized as safe) for food use.
  • INCI name on cosmetic labels: Lactic Acid.
  • CIR-reviewed and found safe within concentration and pH limits.

Popular products containing Lactic Acid

  • The Ordinary Lactic Acid 10% + HA — Entry lactic serumThe Ordinary · Skincare
  • Sunday Riley Good Genes (lactic acid) — Premium lactic treatmentSunday Riley · Skincare
  • AmLactin Daily Moisturizing Lotion (12%) — Body exfoliating lotionAmLactin · OTC drug

Product names and brands are shown for reference and belong to their respective owners.

Lactic vs glycolic

Both are AHAs; glycolic is smaller, penetrates faster, and exfoliates harder; lactic is larger, penetrates gradually, and hydrates while it works. Sensitive skin, dry skin, and acid beginners generally do better with lactic; tolerant skin chasing maximum resurfacing often prefers glycolic. Many routines rotate both.

The NMF connection

Lactic acid is a natural component of the skin's own moisturizing factor, which is why its application supports — rather than strips — the barrier. This dual identity explains its unusually good tolerability-to-efficacy ratio in the acid category.

Frequently asked questions

Can I use lactic acid every day?

At 5% with a tolerant skin, daily is possible; 10% is usually better 2–3 nights weekly. Start slow and watch for over-exfoliation (shininess, stinging).

Is lactic acid safe for sensitive skin?

It is the gentlest major AHA and the usual recommendation for reactive skin — though even lactic deserves patch-testing and gradual introduction.

Does lactic acid lighten skin?

It fades surface pigment through exfoliation and mild tyrosinase effects — a gradual brightening, not a bleaching action.

The bottom line

Lactic acid is the skin's own gentle exfoliant — an AHA that resurfaces and hydrates in one molecule, making it the default entry point for acid newcomers.

References

  1. Lactic acid in dermatology. PubMed Central. https://pubmed.ncbi.nlm.nih.gov/31197009/
  2. Alpha-hydroxy acids: clinical review. PubMed. https://pubmed.ncbi.nlm.nih.gov/29086889/
  3. Lactic acid — Cosmetic Ingredient Review. CIR. https://www.cir-safety.org/ingredients