-
Can you combine ascorbic acid and retinol in an anhydrous glycol + oil emulsion?
Stabilities of ascorbic acid and retinol are pH-dependent in aqueous emulsions (O/W and W/O emulsions). Ascorbic acid is stable in acidic conditions (below its pKa), while retinol is stable in neutral pH conditions. Therefore, ascorbic acid and retinol are often not formulated together in an aqueous system.
When you dissolve ascorbic acid in glycols, ascorbic acid remains largely non-ionized and is more stable than in aqueous systems. When you incubate an ascorbic acid in glycol solution on a pH strip in a sealed chamber (to prevent moisture absorption from the atmosphere), however, it starts showing a pH of around 2.5 after about 30 minutes (initially the pH strip doesn’t change the color). This hints that there is still a little bit of ionization of ascorbic acid in the glycol solvent.
My question is, would this lower level of ionization and acidity of ascorbic acid in the glycol solvent be sufficient to decompose retinol when you combine ascorbic acid + retinol in an anhydrous glycol + oil emulsion? Any chemists here who can comment on this?
Many thanks in advance!
-
1 Reply
-
Good question, but I think you’re overthinking it.
In an anhydrous glycol and oil system, pH doesn’t really apply. pH requires water. If you’re seeing a pH reading after 30 minutes on a strip, it’s likely due to trace moisture or slow absorption from the air, not because the system is truly acidic in a way that affects stability.
Ascorbic acid and retinol can both be unstable, but in this type of system, pH isn’t relevant. If there’s degradation, it’s more likely due to oxidation, not acidity.
So yes, they might interact over time, but not for the reasons you’re assuming. If stability is a concern, use stabilized forms, encapsulation, or just don’t combine them.
Hope that clears it up.
Log in to reply.