Yes, it’s completely normal! In fact, turning yellow is Vitamin C's natural process of oxidization. All Vitamin C products will gradually oxide and turn yellow over time. This means the effectiveness of Vitamin C products diminishes over time, but it is not harmful to continue using on your skin in any way. We recommend keeping Vitamin C products (and other products containing actives) out of sunlight and direct heat so you can keep them fresh as long as possible. You might want to keep the Vitamin C serum in the vegetable drawer in your fridge so you can enjoy a cool Vitamin C serum when applying it in your routine, too.