Glycolic Acid + Other AHAs (Lactic Acid, Mandelic Acid)
Use With Caution
These ingredients can be combined, but require careful timing, lower concentrations, or gradual introduction.
Using multiple AHAs simultaneously offers no additional benefit and increases irritation risk - choose one or alternate.
What the Research Says
Glycolic acid, lactic acid, and mandelic acid all belong to the alpha-hydroxy acid (AHA) family. They share the same fundamental mechanism of action: dissolving the intercellular bonds (desmosomes) between corneocytes in the stratum corneum to promote exfoliation. The primary difference between them is molecular size, which affects penetration depth. Glycolic acid has the smallest molecule and penetrates deepest, lactic acid is intermediate, and mandelic acid is the largest and most gentle.
Using two AHAs at the same time does not provide meaningfully different exfoliation - it simply increases the total acid concentration your skin experiences, which increases the risk of over-exfoliation, irritation, and barrier damage. If a 10% glycolic acid product is not providing sufficient exfoliation, the solution is to adjust the concentration or pH of that single product, not to layer another AHA on top.
That said, there are valid reasons to have multiple AHAs in your regimen if they are used at different times. For example, a gentle daily lactic acid toner combined with a weekly glycolic acid treatment peel is a well-established approach. The key principle is: only one AHA per application, and total weekly exfoliation should not exceed what your skin can tolerate.
Timing & How to Use
Never layer multiple AHAs in the same routine. Choose one AHA per application. If you want to use different AHAs, alternate them: for example, lactic acid on weekdays and glycolic acid on weekends, or a daily low-concentration AHA toner on days you skip your weekly glycolic acid treatment.
Practical Tips
- 1Glycolic acid is the most potent AHA - if it works for you, additional AHAs are rarely needed
- 2Lactic acid is a better choice for sensitive skin or beginners due to its larger molecule size
- 3Mandelic acid is the gentlest option and better for darker skin tones prone to post-inflammatory hyperpigmentation
- 4Multi-acid products are formulated to control total acid concentration - do not add more acid on top of them
References
- Tang SC, Yang JH. Dual effects of alpha-hydroxy acids on the skin. Molecules. 2018;23(4):863.
- Kornhauser A, et al. Applications of hydroxy acids: Classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol. 2010;3:135-42.
- Stiller MJ, et al. Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. J Am Acad Dermatol. 1996;34(3):435-9.
