You can use hyaluronic acid, which helps to keep skin feeling hydrated, and vitamin C together. Hyaluronic Acid is a great humectant and is best layered with a complementing moisturizer depending on the skin type. Just keep in mind not all hyaluronic acid is created equal and many over-the-counter hyaluronic acid products are made of molecules too large for the skin to absorb. Those with acne should only use products tested on a small area of the skin. Ideally, you should consult a licensed esthetician before using hyaluronic acid or vitamin c.