Vitamin C is also notoriously unstable and starts to degrade when exposed to heat, light, and air. So whatever vitamin C product you go with should be in an air tight, dark bottle that gets stored in the refrigerator. Based on all this, I'm sticking with temperamental and delicate as adjectives.
|Source FutureDerm: The Science of Beauty|
Here is something I just learned a few weeks ago: vitamin C's effects on the skin last 72 hours, which means you really don't need to apply it daily. I felt pressured to use up my bottle ASAP due to the limited shelf life (1 year from opening, but then there are those pesky oxidation issues nipping at your heels), so I'm not sure knowing about the 72 hour lasting effects would have slowed me down any. The bottle I purchased from Memebox ($25) had an expiration date of 1/28/16, but it worked well right up to the last drops. It still took me a good 8 months to finish off this bottle using it 3-4 times a week, as I would sometimes forget because it was in the refrigerator. Out of sight, out of mind, you know.
official Ciracle site for $39.30. I just purchased a reasonably priced vitamin C serum from a US brand called Simply Radiant, so I'll have something to compare. I've also heard good things about Drunk Elephants C-Firma Day Serum, but I'm not quite ready to spend $80 to try it out :-)