At a glance
- CAS number
- 50-21-5
- INCI name
- Lactic Acid
- Function
- ph_adjuster, humectant, active, exfoliant
- Typical use level
- 0.5%–12%
- Solubility
- water
- Stable pH
- 2.5–4.5
CAS number and synonyms are sourced from PubChem. Function, usage levels, pH and compatibility are AI-assisted formulation guidance — verify against your supplier's technical data sheet and applicable regulations before use.
Also known as
lactic acid 2-hydroxypropanoic acid DL-Lactic acid 2-hydroxypropionic acid Milk acid Tonsillosan Racemic lactic acid Ordinary lactic acid Acidum lacticum Ethylidenelactic acid Lactovagan Milchsaeure
Compatibility
Works well with:
Glycerin Hyaluronic Acid Niacinamide Sodium Lactate Allantoin Panthenol Aloe Vera Sodium PCA Urea
Use caution with:
Retinol Benzoyl Peroxide Vitamin C (L-Ascorbic Acid) Salicylic Acid Strong Bases
Lactic acid can lower pH significantly, potentially destabilizing other pH-sensitive actives like retinol or causing irritation when combined with other exfoliating acids. Combining with benzoyl peroxide or multiple AHAs increases irritation risk and should be approached with caution. Strong bases will neutralize lactic acid, reducing its efficacy as both a pH adjuster and exfoliant.
Formulation notes
In the EU, leave-on products containing AHAs above 10% (as acid) require a pH ≥ 3.5 and a specific warning label; rinse-off products have separate thresholds. At concentrations above 4-5% with low pH, it functions as a chemical exfoliant (AHA); at lower levels it acts primarily as a humectant and pH adjuster. Sun sensitivity warning may be required at exfoliant-level concentrations. CAS: 50-21-5.
Related ingredients
- Glycolic AcidActive
- Citric AcidPh Adjuster
- Ascorbic AcidAntioxidant
- Mandelic AcidExfoliant
- Phytic AcidChelator
- Sodium GluconateChelator