These are skincare ingredients that help enrich skin's surface, drenching it with revitalizing hydration and keeping it there. Doing so helps keep skin looking and feeling soft, smooth, and supple—especially skin that's persistently dry, tight, and uncomfortable. Daily application of skin-replenishing ingredients keep skin safeguarded from environmental factors that lead to moisture loss and dehydration, and help skin appear younger, more vibrant, and replenished!
There are numerous skin-replenishing ingredients to consider, some of which are naturally present in skin, including hyaluronic acid, ceramides, sodium PCA, glycerin, glycerol, cholesterol, and phospholipids. Other examples of research-proven skin-replenishing ingredients are silicones, petrolatum, triglycerides, omega fatty acids, and exfoliating ingredients like alpha hydroxy acids (AHAs like glycolic acid) and beta hydroxy acid (BHA, salicylic acid).
References for this information:
Journal of the American Academy of Dermatology, July 2014, pages 177-184
Dermatoendocrinology, July 2012, pages 253-258
British Journal of Dermatology, September 2008, pages 567-577
Dermatologic Therapy, May-June 2012, pages 229-233 and Volume 17, Supplemental, 2004, pages 49-56
Journal of Investigative Dermatology, August 2003, pages 231-241
Der Hautarzt, January 1998, pages 6-9