Order leave-on skincare from lowest aqueous pH to highest emulsion viscosity, separating low-pH acids (L-ascorbic acid pH 2.5-3.5, salicylic acid pH 3.0-3.8) from retinaldehyde (pH 5.5-6.5) across AM and PM routines. Buffered ferment filtrates (pH 4.2-5.4) bridge moisture retention without disrupting acid mantle recovery.
Formulation Compatibility Engine
Modern stabilized formulations rarely hydrolyze niacinamide into nicotinic acid at skin temperature.
Sequencing Protocol: Apply aqueous L-Ascorbic Acid first, pause 10 minutes, then layer Niacinamide.
The workbench computes wait times and separation warnings from four physical constants: formulation pH range, acid/base dissociation constant (pKa), solvent polarity, and barrier sensitization load. All calculations execute locally in your browser with zero external telemetry.
| Active Molecule | Optimal Vehicle pH | pKa / Chemistry | Preferred Window | Primary Conflict Trigger |
|---|---|---|---|---|
| L-Ascorbic Acid (10-20%) | 2.5 - 3.5 | pKa 4.17 | Morning (AM) | Retinaldehyde hydrolysis, high-flush niacinamide overlap |
| Retinaldehyde (0.05-0.1%) | 5.5 - 6.5 | Lipophilic aldehyde | Evening (PM) | Concurrent BHA desmolysis or low-pH acid denaturation |
| Salicylic Acid / BHA (1-2%) | 3.0 - 3.8 | pKa 2.97 | Evening (PM) | Additive barrier lipid stripping with L-AA or retinoids |
| Niacinamide (2-5%) | 5.0 - 7.0 | pKa 3.35 (base) | AM & PM | Transient flushing if immediately stacked over pH < 3.5 on reactive skin |
| Ferment Filtrate | 4.2 - 5.4 | Lactate / acetate buffer | AM & PM | Apply after bare-skin low-pH acids if skin is sensitized |
Replaces the retired 2018-2023 Ampersand Serum Finder quiz with a deterministic cosmetic chemistry layering engine. Whereas the original tool matched skin concerns (pigmentation, dehydration, redness, fine lines) across the six ESD serums, this workbench extends the logic to modern active stacking safety.