Humectants used in cosmetics include triethylene glycol, tripropylene glycol, propylene glycol, and PPGs. Other popular humectants in cosmetics include glycerin, sorbitol (sugar alcohol), hexylene and butylene glycol, urea, and collagen. Glycerin is one of the most popular humectants used because it produces the desired result fairly frequently and is low in cost. A category of humectants called nanolipidgels allow skin to retain moisture, but also possess antifungal properties. Scientists are also working to discover different types of humectants; a study published in 2011 concluded that extracts from wine cakes have the potential to be used as a humectant in cosmetics.