A patient brought me her vitamin C last week. It was the colour of weak tea. She'd been using it for three months thinking it was working. By the time most vitamin C reaches you, it's already oxidised. That brown tint isn't a colour, it's rust. L-ascorbic acid is wildly unstable. Preserving it properly is expensive. The right pH, dark glass, vitamin E to protect it. That's why a real vitamin C is never cheap. The question isn't whether to use it. It's which one is right for your skin.