Might not be just one. I do like ascorbic acid - Paula's Choice C15, Vichy Liftactiv +
I have hereditary dark circles (like my mom did) that have gotten more ++
ROC peptide
I always lay a base of something rich in hyaluronic acid (either Hada Labo Premium or +
Empties+
ROC multi correction hydrate and plump is amazing +
Don't have one favourite, it's usually one of the following: Skinceuticals CE Ferulic +
I also ''grew up'' with Skinceuticals serums, since their Primacy and AOX products +
Retinoids might help to some extent since both crepey skin and fine lines tend +
Best is relative but I think PTR doesn't use actual vitamin C but some sort of +