Vitamin C and Retinol
Au says combining Vitamin C and Retinol is one highly common but detrimental mistake. When used on their own, both of these ingredients offer incredible beauty benefits, but as it turns out, using them together could hinder your results. As a good rule of thumb, you should use Vitamin C in the morning and Retinol at night.
"These are both holy grails of skincare and should be used by everyone," Au notes. "But Vitamin C is to be used in the morning. Retinol is to be used in the evening, since our skin does a lot of repairing while we sleep at night."
If you've been combining these ingredients, it's time to make some changes to your skincare routine—you likely haven't seen the results you've been hoping for, and there's a good reason for that. Au explains that when you put these two together, "the vitamin C will chemically deactivate retinol, making it ineffective."
It isn't just the potency of the retinol that's at risk; this combo can also cause irritation. "Retinol helps build collagen and thickens the skin with cell turnover, so using it with a low pH level acid like Vitamin C can cause irritations," Au warns. "There should be no reason they are used together."
However, while applying these ingredients at the same time is generally a no-go, Au says they should both be staples in your skincare cabinet. "There is no doubt that retinol and vitamin C should be used by everyone regardless of skin type and skin concerns," she states.
Additionally, there may even be instances where these two ingredients are combined in one medical grade skincare product for a good reason. "While the rule of thumb is that they should never be used together, once in a blue moon you may see an innovative medical grade formulation where there are both of those ingredients together," Au says. "In those very unique instances, that is when you have to trust the science and the medical studies that are backing that product because these are formulated in a way where they will work."
But when it comes to your day-to-day serums, keep these two separate. "In all other instances, C during the day. Retinol at night," Au emphasizes. "Make it your mantra!" Noted!