Pure Vitamin C (L-Ascorbic Acid) is a highly effective antioxidant that is notoriously unstable. Due to its delicate makeup, L-Ascorbic Acid is vulnerable to oxidation when exposed to light, heat, or even just air, making some level of discoloration almost inevitable over time.

Fortunately, Vitamin C retains most of its potency through the first several phases of oxidation, which means it’s still both efficacious and perfectly safe to use. A champagne or straw-colored Vitamin C serum is completely normal and still provides your skin with a potent dose of antioxidants.

Here is a cheat sheet to show the level of discoloration relative to the serum’s efficacy.

Here are helpful tips to slow that oxidation and ensure the product lasts longer:

1. Always tightly close the lid.

Oxidation is primarily caused by oxygen (hence the name). When using a Vitamin C serum, try to limit the amount of oxygen that gets into the bottle. Tightly close the lid immediately after applying.

2. Store it in the fridge

Keeping Vitamin C in a cool, dark place is essential because it’s very temperature-sensitive. Plus, storing serums in the fridge helps give a cool, refreshing effect when applied.

3. Avoid light exposure

Light exposure can cause rapid oxidation, so always store your serum in a dark place. If your fridge is too inconvenient, always opt for a dark cabinet or bathroom drawer.

4. Vitamin C won’t last forever

Vitamin C serums typically last about 3 years from production date, but once the bottle is opened and exposed to the elements, a usual lifespan is 2-4 months. Take the measures mentioned above to ensure your serum has a long, potent lifespan.