Lactic Acid

What is it?

Lactic acid is an alpha-hydroxy acid (AHA) that also occurs naturally as a component of the skin's natural moisturizing factor; its L-isomer specifically has been shown to stimulate ceramide synthesis in the skin barrier.

What does it do?

Commonly used as a gentle exfoliant and humectant; a controlled mechanistic study found the L-lactic-acid isomer specifically (not the D-isomer) significantly increased keratinocyte ceramide production and improved stratum corneum barrier function.

How to use

Typically formulated at 5%-12% for leave-on exfoliating products.

Use with caution

• Retinol — Space out use

  Combining a retinoid with a direct AHA in the same routine compounds irritation and dryness.

  Use on alternating nights.

• Glycolic Acid — Space out use

  Both are direct AHAs — combining them adds exfoliation intensity without a clear added benefit over using one at an appropriate strength.

  Choose one AHA per routine rather than stacking both.

Real products containing this

• AHA 30% + BHA 2% Peeling Solution — The Ordinary

Sources