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Lactic acid

Lactic acid is an alpha hydroxy acid (AHA) that does two jobs in skincare. It exfoliates the skin surface, and it binds water, because skin already makes lactate as part of its own moisturizing factor. Like every AHA, it increases sun sensitivity while in use.

At a glance

  • Evidence level A. Published research on the ingredient itself.
  • What it is. A three-carbon alpha hydroxy acid, made today mostly by fermentation of sugars.
  • What it does. Surface exfoliation and moisture binding. Skin feels smoother in published studies.
  • Caution. Increases sun sensitivity. Use sunscreen daily while using it and for a week afterwards.

What it is

Lactic acid is named for milk, where it was first identified, but cosmetic grades are produced by fermentation. It exists in two mirror-image forms, L and D. Skin makes the L form, and some of the research separates the two.

It belongs to the alpha hydroxy acids. As with the rest of the family, concentration and the finished pH together set how active it is. At very low levels, lactic acid is also used simply to bring a formula to the right pH, which is a different job from exfoliation.

Lactic Acid/Glycolic Acid Copolymer is a separate ingredient: a polymer built from the two acids, with no free-acid action.

What it does in skincare

Exfoliation. Like other AHAs, lactic acid weakens the bonds between dead cells in the outer layer of skin, so they shed more evenly. Skin feels smoother and reflects light more evenly.

Moisture binding. Lactate is one of the water-binding components of natural moisturizing factor, the mix of small molecules inside surface skin cells that holds water. A formula containing lactic acid adds a substance skin already uses for that purpose. This is why lactic acid is often described as the more hydrating of the common AHAs.

Evidence

The studies below describe the ingredient itself.

Rawlings and Harding reviewed how natural moisturizing factor, including lactate, keeps the outer layer of skin hydrated. Smith studied lactic acid applied to skin at two concentrations and reported changes confined to the epidermis at the lower strength, and changes in both epidermis and dermis at the higher strength.

Rawlings and colleagues compared the L and D forms in laboratory and skin studies. They reported that L-lactic acid increased ceramide production by skin cells in culture, and that its topical use improved measurements of the skin barrier. This is laboratory and small-study evidence on the ingredient form.

The Cosmetic Ingredient Review assessed lactic and glycolic acid together in 1998. It concluded they are safe in consumer products at up to 10% and a final pH of 3.5 or higher, when the product avoids increasing sun sensitivity or its directions call for daily sun protection. FDA's labeling guidance for AHA cosmetics recommends a sunburn alert for the class.

Use and caution

Sun-sensitivity notice. FDA recommends this statement for cosmetics containing alpha hydroxy acids:

Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.

How to combine acids with sun protection: acids and sun sensitivity.

  • Patch test first. See patch testing and declared allergens.
  • Start with a few evenings a week and build up.
  • Stop if stinging persists or redness stays.
  • Avoid the eye area and broken skin.
  • Keep to one exfoliating product per routine unless a professional advises otherwise.

In Vegalab products

The Brightening NanoSerum sealed vial set lists lactic acid together with glycolic acid and mandelic acid. The sun-sensitivity notice above applies to it.

References

  1. Rawlings AV, Harding CR. Moisturization and skin barrier function. Dermatol Ther. 2004;17(Suppl 1):43-48.
  2. Smith WP. Epidermal and dermal effects of topical lactic acid. J Am Acad Dermatol. 1996;35(3 Pt 1):388-391.
  3. Rawlings AV, Davies A, Carlomusto M, et al. Effect of lactic acid isomers on keratinocyte ceramide synthesis, stratum corneum lipid levels and stratum corneum barrier function. Arch Dermatol Res. 1996;288(7):383-390.
  4. Cosmetic Ingredient Review. Final report on the safety assessment of glycolic acid, ammonium, calcium, potassium, and sodium glycolates, methyl, ethyl, propyl, and butyl glycolates, and lactic acid, ammonium, calcium, potassium, sodium, and TEA-lactates, methyl, ethyl, isopropyl, and butyl lactates, and lauryl, myristyl, and cetyl lactates. Int J Toxicol. 1998;17(Suppl 1):1-241.
  5. US Food and Drug Administration. Guidance for Industry: Labeling for Topically Applied Cosmetic Products Containing Alpha Hydroxy Acids as Ingredients. January 2005.
  6. Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol. 2010;3:135-142.
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