What Is Hyaluronic Acid Serum and Why It Works Few skincare ingredients are as universally loved—or as well studied—as a high-quality Hyaluronic Acid Serum. Hyaluronic acid (HA) is a naturally occurring polysaccharide found in the skin, eyes, and connective tissues, prized for its extraordinary ability to bind and hold water. As a powerful humectant, it…