Free Acid Value
Free Acid Value — the percentage of an exfoliating acid in a formula that is present in its active, unbound acid form rather than its neutralized salt form. It is a more meaningful measure of a product's exfoliating strength than the total acid concentration alone, because only free acid drives exfoliation.
Key points
- Free acid value is determined by the total acid concentration together with the formula's pH.
- As pH rises toward the acid's pKa, more of the acid shifts into its inactive salt form.
- A product can list a high total acid percentage yet have a lower effective free acid value.
- Free acid value helps compare the real potency of different exfoliating acid products.
Frequently asked
Why does free acid value matter more than total acid percentage?
Only the free, un-neutralized acid actively exfoliates, so free acid value reflects a product's true strength better than the labeled total concentration.
How does pH affect free acid value?
Lower pH keeps more of the acid in its active free form, while higher pH converts more of it into a less active salt, reducing the free acid value.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
