THE PH LEVELS OF CHEMICAL EXFOLIANTS
Free Acid Value and Bioavailability
Understanding pKa and Free Acids
Don't be fooled by high percentages on a label. A 10% Glycolic Acid product formulated at a pH of 4.5 is mostly neutralized and vastly less effective than a 5% Glycolic Acid formulated at a pH of 3.2. This relies on understanding a molecule's pKa value.
The pKa is the pH level at which exactly 50% of the acid is in its free (active) state, and 50% is in its ionized (neutralized/salt) state. To get maximum cellular desquamation (exfoliation), the formulation's pH must be close to or lower than the acid's pKa.
Alpha Hydroxy Acids (AHA)
Glycolic Acid (Molecular Weight: 76.05 g/mol, pKa: 3.83). Due to its low molecular weight, it penetrates rapidly, dissolving the desmosomes that hold dead skin cells together. Ideal formulation pH is between 3.0 and 4.0.
Lactic Acid (MW: 90.08 g/mol, pKa: 3.86). Larger than glycolic, penetrating slower, making it gentler. It uniquely increases natural moisturizing factors (NMF) within the skin.
Beta Hydroxy Acids (BHA)
Salicylic Acid (MW: 138.12 g/mol, pKa: 2.97). Unlike AHAs which are water-soluble, BHA is lipid (fat) soluble. This allows the molecule to bypass the skin's surface lipids and penetrate directly into the sebaceous gland to dissolve sebum.
Optimal efficacy occurs at a pH between 3.0 and 3.5.