
How to Choose a Vitamin C Serum: Forms, Concentrations, and Red Flags
Choose a vitamin C serum by form first, percentage second.
The ingredient list is the most honest part of any beauty product, and this collection teaches you to read it. We cover the actives that dominate skincare marketing — retinoids, vitamin C, exfoliating acids, humectants — plus the label terms that sound regulated but aren't. Each explainer sticks to what mainstream cosmetic science supports, at what concentrations, and for whom. We don't promise results, and we flag ingredients that commonly need patch-testing or a slow introduction. The goal is simple: you should be able to judge a product before you pay for it.

Choose a vitamin C serum by form first, percentage second.

Retinol and retinal (retinaldehyde) are both over-the-counter retinoids, but retinal sits one conversion step closer to retinoic acid, the form skin.

Skincare ingredient lists (INCI lists) rank ingredients above roughly 1% in descending order, so the first five tell you what a product fundamentally is.