Open most Vitamin C serums after a few weeks in an Indian summer and you’ll see it: a yellow-to-brown tint. That colour is oxidized L-Ascorbic Acid. The molecule is unstable above roughly 35°C, and it degrades into useless — sometimes irritating — byproducts.
The fix isn’t refrigeration. It’s chemistry. 3-O-Ethyl Ascorbic Acid delivers the same brightening and antioxidant activity but holds stable through 90 days at 43°C. We test every batch to prove it.
If your serum has turned yellow, you’re applying a placebo. Read the box. Check the form of Vitamin C.
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