AHA vs BHA: which chemical exfoliant is right for you

AHAs (glycolic acid, lactic acid, mandelic acid, malic acid) are water-soluble. They dissolve the bonds between dead skin cells at the surface, smoothing texture, brightening tone, and softening fine lines over weeks. Glycolic is the smallest molecule and the most-potent (best for ageing and pigmentation). Lactic is mid-size, gentler, and adds hydration. Mandelic is the largest and gentlest, well-suited to sensitive skin and darker skin tones where glycolic can cause post-inflammatory hyperpigmentation.

BHAs (salicylic acid is the only commonly used BHA in skincare) are oil-soluble. They penetrate into the pore lining and break up the oil-and-dead-skin plugs that cause blackheads and acne. The oil solubility is the key feature: water-soluble AHAs cannot reach the inside of a pore the way salicylic can.

Choose AHA if: your main concern is surface texture, dullness, fine lines, uneven tone, sun damage, or post-acne pigmentation. AHAs are the right tool for the visible surface layer. Glycolic 5-10% is the workhorse concentration. Lactic 5-10% is gentler. Mandelic 10% is the recommendation for sensitive or melanin-rich skin.

Choose BHA if: your main concern is blackheads, breakouts, oily T-zone, or pore congestion. Salicylic acid 0.5-2% is the standard concentration. Apply only to affected areas if dryness is a concern; whole-face application works for moderate cases.

Use both if: you have combined concerns (uneven tone AND breakouts). Alternate nights, AHA on tone-priority nights and BHA on breakout-priority nights. Do not use both in the same routine; the combined acid load is too much for most skin.

Two to three times per week is the standard cadence for most people. Daily exfoliation almost always over-exfoliates and produces the 'glassy-but-irritated' look that signals barrier damage. Less is more; consistent twice-weekly exfoliation outperforms aggressive daily acids for nearly every concern.

Always use SPF the morning after any chemical exfoliant. AHAs in particular significantly increase photo-sensitivity. Skipping daily sunscreen while using acids cancels most of the benefit and accelerates the pigmentation you were trying to address.