Mandelic acid, an AHA that can be synthesized or derived from almonds, stands out from other alpha hydroxy acids because of its size. Its molecule is roughly twice as large as glycolic acid's. That larger structure means it penetrates skin more slowly and evenly, which translates into a gentler exfoliating experience, well suited to sensitive or rosacea prone skin that might not tolerate glycolic acid. At the right pH (3 to 4) and concentrations of 5% or higher in leave on formulas, it works as an effective exfoliant despite being milder than its counterparts.
For fading uneven tone, including post breakout marks, melasma, and sun induced dark spots, mandelic acid may actually have a slight edge over other AHAs. It's well tolerated across all skin tones, and because it's soluble in both oil and water, it can address texture and firmness at multiple levels. It also pairs well alongside a BHA or another AHA in the same routine.
One caveat: at peel strength concentrations of 30% or higher, mandelic acid has been shown to increase sebum production. That's not ideal if you're oily, but for dry skin dealing with both discoloration and dehydration, that same effect can be a welcome bonus.
Mandelic Acid References
Journal of Cosmetic Dermatology, February 2023, pages 517–528; and February 2020, pages 393–399 | Molecules, September 2022, pages 1–11 | Journal of the American Academy of Dermatology, December 2020, Volume 83, Issue 6 and September 2018, pages 503-518 | Dermatologic Surgery, March 2016, pages 384-391; and January 2009, pages 59-65 | Advances in Dermatology and Allergology, June 2013, pages 140-145
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