Your easiest option would be to separate the two, using vitamin C in the morning and retinol at night. If using them together, wait at least 30 minutes between application, so vitamin C has time to absorb. It’s best to apply vitamin C before retinol, as vitamin C has a lower pH than retinol. Once your skin absorbs the vitamin C serum, your As vitamin C is well known for its instability, it’s important to keep an eye — and a nose — out for any changes in the serum’s color or smell from the time it was opened. “Vitamin C serum should be a clear liquid; when it turns orange/brown, that’s a sign that the serum has oxidized and has lost some of its efficacy,” Casey said. Incorporating vitamin C serum into your skincare routine as a preventative measure may be especially important if you’re a person of color, since, again, we’re more prone to hyperpigmentation. So, it only makes sense that one of the most coveted serums for women over 50 would be a vitamin C serum — the iconic Truth Serum from Olehenriksen. A powerful blend of vitamin C and collagen, this anti-aging formula is antioxidant rich and known for its ability to help brighten, firm, and hydrate skin all day long. MBp0.