The first-generation chemical exfoliants — glycolic acid (the smallest, fastest-penetrating AHA) and salicylic acid (BHA for oily/acne-prone skin) — dominate skincare conversations. But a second generation of acids offers meaningful clinical benefits with significantly improved tolerability profiles — making them the preferred choice for sensitive skin, rosacea, and those who cannot tolerate glycolic acid's rapid penetration.
Lactic Acid: The Gentle AHA with Added Benefits
Lactic acid is an AHA with a larger molecular size than glycolic acid — penetrating more slowly into the stratum corneum, producing comparable keratolytic effects at equivalent concentrations with significantly less irritation. Key differentiator: lactic acid is a natural component of the skin's natural moisturizing factor (NMF) — it acts as both an exfoliant and a humectant, increasing skin hydration simultaneously with exfoliation. Concentration guidance: 5–10% for daily use, 10–20% for weekly treatment exfoliation. Clinical evidence: equivalent to glycolic acid for treating ichthyosis and xerosis (dry skin conditions) in RCTs, with superior tolerability. Preferred over glycolic for: dry skin combined with rough texture, beginners to chemical exfoliation, eczema-adjacent skin in remission.
Mandelic Acid and PHAs
Mandelic acid (alpha-mandelic acid, derived from almonds): the largest common AHA — slowest penetration, greatest tolerability, making it the gentler choice for darker skin tones where irritation-induced PIH is a significant concern. Additional benefits: mild antibacterial properties (relevant for acne) and unique lipid-soluble character (intermediate between AHA and BHA — can penetrate oily pores better than other AHAs). Clinical evidence: comparable to glycolic acid for comedonal acne in split-face RCTs, with dramatically lower irritation. Polyhydroxy acids (PHAs — gluconolactone, lactobionic acid, galactose): next-generation AHA derivatives with 4 hydroxyl groups vs. AHA's 1–3 — much larger molecules (gluconolactone MW 178 vs. glycolic MW 76), minimal skin penetration, primarily surface-level exfoliation. PHAs are the only chemical exfoliants with evidence supporting use during rosacea — they exfoliate without worsening barrier dysfunction, and lactobionic acid has demonstrated antioxidant and wound healing properties. For clinical skin management programs, our skin care catalog includes complementary barrier repair and moisturizing products appropriate for acid-using skin types.
