# Lactic acid

Source: https://theconstantbeauty.com/ingredients/lactic-acid/
Retrieved for: theconstantbeauty.com
Publisher: The Constant (theconstantbeauty.com). Cite as "The Constant".
Generated: 2026-09-16T18:28Z

- **INCI name:** Lactic Acid
- **Common name:** Lactic acid
- **Typical use range:** 5–10%
- **Evidence tier:** literature-backed
- **Functions:** exfoliant, humectant

## What it does

Lactic acid is an alpha hydroxy acid (AHA) and, like PCA, a component of the skin's natural moisturising factor. Its molecule is larger than glycolic acid's, so it moves into the skin more slowly. In practice that means a milder, more predictable exfoliation and a lower likelihood of stinging.

At the surface it loosens the bonds holding dull, dead cells in place so they shed more evenly. The result over a few weeks is smoother texture, a brighter look and a more even-looking tone. Unusually for an exfoliant it is also a humectant, so a well-formulated lactic acid product leaves the skin feeling hydrated rather than tight.

The Cosmetic Ingredient Review concluded that AHAs are safe in consumer leave-on products at up to 10% at a pH of 3.5 or higher, with directions for daily sun protection. Exfoliating acids increase sun sensitivity, so a broad-spectrum sunscreen every morning is part of using them properly.

## Notes

Lactic acid is an alpha hydroxy acid (AHA) and, like PCA, a component of the skin’s natural moisturising factor. Its molecule is larger than glycolic acid’s, so it moves into the skin more slowly. In practice that means a milder, more predictable exfoliation and a lower likelihood of stinging.

At the surface it loosens the bonds holding dull, dead cells in place so they shed more evenly. The result over a few weeks is smoother texture, a brighter look and a more even-looking tone. Unusually for an exfoliant it is also a humectant, so a well-formulated lactic acid product leaves the skin feeling hydrated rather than tight.

The Cosmetic Ingredient Review concluded that AHAs are safe in consumer leave-on products at up to 10% at a pH of 3.5 or higher, with directions for daily sun protection. Exfoliating acids increase sun sensitivity, so a broad-spectrum sunscreen every morning is part of using them properly.

## Used in

- [Multi-Active Complex Face Serum](https://theconstantbeauty.com/product/multi-active-complex-serum/)

## References

1. CosIng, Lactic Acid (EU cosmetic ingredient database) <https://ec.europa.eu/growth/tools-databases/cosing/>
2. PubChem, Lactic acid (CID 612) <https://pubchem.ncbi.nlm.nih.gov/compound/612>
3. Cosmetic Ingredient Review. Final report on the safety assessment of glycolic acid, lactic acid and their salts and esters. Int J Toxicol. 1998;17(Suppl 1):1–241.
4. US FDA. Guidance for industry: labeling for cosmetics containing alpha hydroxy acids.