Is it necessary to refrigerate Vitamin C?

It's not necessary to refrigerate vitamin c (some brands actually recommend against it). The reason why people to refrigerate it is to delay oxidization - if you are using L-Ascorbic Acid it can oxidize quickly and reduce effectiveness but if you are using a derivative it is more stable and less likely to occur.

It’s not, but it may help it not to oxidize. However, i use vit c every day and so a serum usually lasts me shorter than 3 months and i never had a problem with oxidation. But if you keep your ascorbic acid serums open for more than 3-4 months, then it migth be beneficial to keep it in the refrigerator. But you should definitely keep it in the dark or in the shade! Here are some good ones:

It is not necessary. It could help with slowing oxidation but its not a must. I have used my vitamin c for about 4 months and it’s not oxidised at all. I just leave it in its paper packaging box and in a dark place.

Its unnecessary. Unstable vit c may need to refrigerated bcz it can change the color and perhaps decreasing vit c quality . But nowdays many brands has a stable vit c formulated and prevent oxidized probability with darken packaging . My fav vit c is from votre peau , one of local brand in my country .

No. Actually, putting any skincare products are not required to be put in the fridge.