If your skin needs hydration, the optimal order for applying niacinamide and hyaluronic acid is to start with hyaluronic acid first, followed by niacinamide. This allows the hyaluronic acid to penetrate the skin more deeply and provide maximum hydration, while the niacinamide can work its magic on the surface of the skin. If you have oily skin, you can apply niacinamide first to maximize its benefits for reducing pore size, regulating sebum production, and fighting redness and irritation.