L-ascorbic acid starts degrading the moment a vitamin C serum is manufactured. Here is the actual chemistry behind oxidation, and how it should change the way you buy and store these products.
I once owned eleven serums at the same time, layered four a night, and had a vitamin C bottle quietly oxidize for weeks without me noticing. Here's what changed when I stopped — and the few serums that actually earned a repurchase.
Serums are where your routine actually does its work. But with hundreds of options promising everything, most people are buying the wrong ones. Here's the complete guide — and the 7 best serums of 2026.