I'm not buying that bullshit, either. I will say that Vitamin C products "go off" if they are not stored properly. I have found that the best one ever (also the least irritating) is The Ordinary's L-Ascorbic Powder that you add to whatever serum you want. (Not retinol). It's micronised, it lasts forever, and a leeeetle goes a very long way. (I do suggest starting VERY small if you can get it, and working up. It comes with a scoop, and you only need about 1/4-1/2 a scoop to do your whole décolleté, neck and face.) It is very hard to get these days, but it's, very effective and it's CHEAP! Failing that, I also really, really love this product, which is very similar, but not so cheap. It is the same powder, and it comes suspended over a rosehip oil-based serum. It's lovely, but it's a booster product, and it's not intended to last long enough to go off. This thing comes in tiny, weeny bottles, and for this reason, I think it's over-priced. trilogyproducts.co.uk/products/vitamin-c-booster-treatment. If you can get the Ordinary Powder (or another micronised L-Ascorbic Acid Powder) do that, instead!