A substance that promotes the retention of moisture. A type of hydrating ingredient found in moisturizers that actually draws water into the skin, but doesn’t necessarily keep it there. Common ingredients like glycerin and hyaluronic acid are humectants. This class of moisturizing ingredients pulls water from the atmosphere into the top layer of the skin. Humectants are frequently used in cosmetics as a way of increasing and maintaining moisture in the skin and hair, in products including shampoo, conditioner, frizz serum, lotions, creams, lip treatments, cleansers, after-sun lotion, and some soaps or body lotions. As hygroscopic moisturizers, humectants work by attracting water to the upper layer of the skin (stratum corneum). All humectants have common hydroxyl groups which allow them to participate in hydrogen bonding and attract water. This process attracts moisture from the outer layer of the skin or, in high humidity, from the atmosphere. The moisture is then trapped against the epidermis or the shaft of the hair, depending on where the humectant is applied.
Various humectants have different ways of behaving because they differ in water binding capacity at different humidities.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. Humectants have been added to skin moisturizing products to treat xerosis. Some moisturizers tend to weaken the skin barrier function, but studies on xerosis have proven that moisturizers containing humectants increase desired moisturizing effects on the affected area without damage to the skin barrier function. In this xerosis treatments study, some "smarting and stinging" was also reported from the use of humectant-rich treatment products. When the humectant glycerol was added to soaps for the cleansing of wounds, similar effects were found. There was an increase in moisture in the areas that the soap was applied, however, "further consideration of conditioning the use of glycerol to improve the absorption of exudates from wounds for an advanced wound healing is needed. The healing properties of humectants are therefore uncertain. Humectants are also added to toothpaste (dentifrice) to stop the product drying out and cracking in the tube. Sorbitol is commonly used as this also contributes a sweet flavour to the toothpaste without contributing to tooth decay.
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