Humectant is a hygroscopic substance used to keep things moist.  They are important cosmetic ingredients allowing to prevent loss of moisture thereby retaining the skin’s natural moisture. Some compounds also have the ability to actively attract moisture. Humectants are key ingredients in most skin care products but are also often used in hair care products to volumize the hair by attracting moisture which expands the hair shaft. There is a large variety of very different compounds providing moistursing effects including proteins, acids, polysaccharides, and various small molecules (e.g. glycerine, sorbitol, urea, aloe vera etc.).