Also called glycerol or glycerine; it is present in all natural lipids (fats), whether animal or vegetable. It can be derived from natural substances by hydrolysis of fats and by fermentation of sugars. It can also be synthetically manufactured. Whether natural or synthetic, glycerin is a humectant and extremely hygroscopic, meaning it readily absorbs water from other sources. So, in part, glycerin works because of its ability to attract water from the environment and from the lower layers of skin (dermis) increasing the amount of water in the surface layers of skin. Another aspect of glycerin’s benefit is that it is a skin-identical ingredient, meaning it is a substance found naturally in skin. In that respect it is one of the many substances in skin that help maintain the outer barrier and prevent dryness or scaling.
Humectants such as glycerin have always raised the question as to whether or not they take too much water from skin. Pure glycerin (100% concentration) on skin is not helpful and can actually be drying, causing blisters if left on too long. So a major drawback of any humectant (including glycerin) when used in pure form is that they can increase water loss by attracting water from the lower layers of skin (dermis) into the surface layers of skin (epidermis) where the water can easily be lost into the environment. That doesn’t help dry skin or any skin type for that matter. For this reason, glycerin and humectants in general are always combined with other ingredients to soften skin. Glycerin combined with other emollients and/or oils is a fundamental cornerstone of most moisturizers. (Source: Skin Therapy Letter, February 2005, pages 1-8) What about products touting their high levels of glycerin? There is no research showing higher amounts of glycerin have any increased benefit for skin. The research shows a combination of ingredients including glycerin, dimethicone, petrolatum, antixoxidants, fatty acids, lecithin, among many others, are excellent for helping skin heal, reduce associated dermatitis, and restore normal barrier function if used on an ongoing basis (Sources Clinical Experiments in Dermatology, January 2007, pages 88-90; American Journal of Clinical Dermatology, April 2003, pages 771-788; Journal of Molecular Medicine, February 2008, pages 221-231; British Journal of Dermatology, July 2008, pages 23-34; Skin Pharmacology and Physiology, January 2008, pages 39-45). When properly formulated, glycerin shores up the skin’s natural protection by filling in the area known as the intercellular matrix and by attracting just the right amount of water to maintain the skin’s homeostasis. There is also research indicating that the presence of glycerin in the intercellular layer helps other skin lipids do their jobs better (Sources: American Journal of Contact Dermatitis, September 2000, pages 165–169; and Acta Dermato-Venereologica, November 1999, pages 418–421).