Yes, you can use hyaluronic acid and vitamin C together in your skincare routine. The combination of hyaluronic acid and vitamin C can be beneficial for your skin. Hyaluronic acid helps to hydrate the skin, while vitamin C has antioxidant properties and brightens the skin. However, it's best to use them separately, or apply them at different times of day, as combining them in high concentrations may cause skin irritation in some individuals.