The Molecular Architecture: AHA vs. BHA vs. PHA
1. Alpha-Hydroxy Acids (AHAs - Glycolic, Lactic): Water-soluble molecules that target the surface stratum corneum. Glycolic acid has the smallest molecular weight (76 Da), allowing it to penetrate rapidly and deeply to stimulate fibroblast collagen, but with higher potential for stinging. Lactic acid (90 Da) penetrates more gradually and functions as a natural humectant.
2. Beta-Hydroxy Acid (BHA - Salicylic Acid): Oil-soluble (lipophilic) molecule (138 Da). Because it dissolves in sebum, it bypasses the surface and dives deep into the sebaceous follicle, dissolving hardened sebum plugs, clearing blackheads, and exerting natural anti-inflammatory actions.
3. Poly-Hydroxy Acids (PHAs - Gluconolactone, Lactobionic Acid): Second-generation AHAs with massive molecular weights (178 Da). Because of their large size, they cannot penetrate rapidly into living skin layers, working exclusively on the very outer dead keratin scales with virtually zero risk of burning or stinging—making them the gold standard for eczema and rosacea-prone skin.
The pH & Free Acid Calculation
A product can claim '10% Glycolic Acid', but if its formulation pH is buffered above 4.5, virtually all the acid molecules dissociate into inactive salts. To effectively dissolve desmosomes, chemical exfoliants must operate in a pH range of 3.4 to 4.0.
Never layer multiple strong acids on top of one another on the same night. Use your BHA 2 nights a week for pores, your AHA 1 night for brightening, and dedicate remaining nights to barrier recovery with ceramides and peptides.