The SkinCueticals C+AHA I purchased, what, about 6 weeks ago has oxidised. It has in the space of a week gone from a light champagne colour to a *really* dark brown. This is despite the fact it has been stored in the fridge!

SkinCeuticals claim that their serums are still fine when that happens, but I'm not convinced about that at all. I'm not even a quarter of the way through the bottle which is annoying. I'm so glad I only purchased the small one though!