Fingernails and cuticles always turn nicotine-y yellow on me after a while whenever I use vitamin C. I guess I’m too sloppy washing my hands after distributing it on my face

1:3 or 1:4

On the ceramide complex — readers asking about adding ceramides to other serums should know that the 3:1:1 molar ratio of ceramides to cholesterol to free fatty acids is critical. Most commercial ceramide complexes are pre-blended at approximately this ratio, but it’s worth checking with your supplier.

One thing that might help readers who experience unexpected flushing or tingling: it’s almost always a niacinamide purity issue, not a pH issue. Niacinamide powder that contains residual nicotinic acid above about 0.3% will cause transient vasodilation in some users. If your supplier’s COA doesn’t separately list nicotinic acid content, that’s a red flag. A good cosmetic-grade niacinamide should specify both overall purity (ideally ≥99.5%) and nicotinic acid as a named impurity.

On the panthenol in formulation #2 — worth flagging for readers that panthenol comes in two forms: D-panthenol and DL-panthenol. Only the D-form converts efficiently to pantothenic acid (the biologically active form that feeds into Coenzyme A production). DL-panthenol contains roughly 50% of the inactive L-form, so you’d need double the concentration to get the same effect. Most cosmetic-grade powder is D-panthenol, but it’s worth checking because the price difference is minimal and the efficacy difference is real.

Marie’s point about ferulic acid being unnecessary here is spot on — it’s the water that creates the oxidation pathway, not the L-ascorbic acid itself in isolation.

For anyone who is working with a water-based vitamin C formulation though and wondering about adding ferulic acid: the mechanism is worth understanding. Ferulic acid doesn’t just “stabilize” vitamin C in some vague way. It works as part of a cyclic antioxidant regeneration network. When L-ascorbic acid neutralizes a free radical and becomes oxidized (dehydroascorbic acid), vitamin E can donate a hydrogen atom to regenerate it — but then vitamin E itself becomes a tocopheroxyl radical. Ferulic acid regenerates that oxidized vitamin E back to its active form. So you get a chain of regeneration: ferulic → vitamin E → vitamin C, each one restoring the previous one.

The well-known Pinnell study showed that adding 0.5% ferulic acid to a 15% L-ascorbic acid + 1% vitamin E solution roughly doubled the photoprotective effect. But that ratio matters — ferulic acid at higher concentrations doesn’t necessarily mean better results, and it needs to be formulated at pH below 3.5 to remain in its unionized (absorbable) form. Something to keep in mind for anyone formulating a CEF serum.