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.
FAQ
Why does my vitamin C serum turn yellow or brown?
That colour is oxidised vitamin C. Pure L-ascorbic acid is unstable, especially above about 35°C, and on contact with heat, air and light it degrades — the yellow-to-brown tint is the visible sign it’s breaking down into less useful, sometimes irritating, byproducts.
Is a yellow vitamin C serum still effective?
Largely no. Once it has oxidised and darkened, much of its brightening and antioxidant activity is lost — you’re applying something closer to a placebo. Check the colour and the form of vitamin C listed on the label.
Does keeping vitamin C in the fridge stop it oxidising?
Refrigeration can slow oxidation a little, but it doesn’t solve the underlying instability of L-ascorbic acid in a hot climate. The more reliable fix is chemistry — choosing a heat-stable derivative rather than relying on storage.
Which form of vitamin C is stable in Indian heat?
Derivatives such as 3-O-Ethyl Ascorbic Acid deliver similar brightening and antioxidant benefits while staying stable through heat that would degrade pure L-ascorbic acid — which is the form we build with, and test for stability.