Can You Mix Glycolic Acid and Lactic Acid?

Why

Glycolic and lactic acid do the same job by the same route. Both are AHAs that loosen the bonds between dead surface cells (corneocytes) so they shed, revealing smoother skin. The practical difference is molecule size. Glycolic acid is the smallest AHA at about 76 daltons, so it penetrates fast and deep and hits hardest. Lactic acid is larger at around 90 daltons, penetrates more slowly, and doubles as a humectant that draws water into the skin, which makes it gentler and more hydrating. Because they share one exfoliation pathway, using both as separate strong products does not add a new benefit; it simply doubles the dose of the same action. That is how people reach over-exfoliation: tight, shiny, stinging skin, then flaking and breakouts as the barrier gives out. Both also lower the skin surface pH and raise UV sensitivity. A well-formulated product that combines them is calibrated as one exfoliating step, so the risk lies in unplanned stacking, not in the pairing itself.

How to combine them

Treat glycolic and lactic acid as one exfoliation slot, not two. If you like a product that already blends them, use it as your single acid step and build the rest of the routine around recovery. If you own separate products, do not layer them the same night. A gentle plan is lactic acid on the nights you want hydration with mild resurfacing, and glycolic on the nights you want a stronger polish, never back to back. Always apply to dry skin, follow with a barrier moisturiser, and start twice a week before increasing. Because both raise sun sensitivity, broad-spectrum SPF 30+ every morning is non-negotiable. If your skin is sensitive, choose lactic acid alone; it delivers most of the glow with less sting.