— § 01
What retinol actually is.
Retinol is the alcohol form of vitamin A. Inside the keratinocyte it is oxidised first to retinaldehyde, then to retinoic acid — the same molecule prescription tretinoin delivers directly. That two-step conversion is why retinol is slower to act and gentler on the barrier: only a fraction of what you apply ever becomes the active species.
Decades of formulation work have built around that limitation: encapsulation, anhydrous vehicles, and slow-release polymers that protect the molecule from oxidation and meter its conversion. A well-formulated 0.5% can outperform a poorly-formulated 1.0%. Concentration on the label is necessary but not sufficient.