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A humectant is a hygroscopic substance. It is often a molecule with several hydrophilic groups, most often hydroxyl groups, but amines and carboxyl groups, sometimes esterified, can be encountered as well; the affinity to form hydrogen bonds with molecules of water is crucial here.
Since hygroscopic substances absorb water from the air, they are frequently used in desiccation. When used as a food additive, the humectant has the effect of keeping the foodstuff moist. Humectants are sometimes used as a component of antistatic coatings for plastics. Humectants are also found in many cosmetic products where moisturization is desired, including treatments such as moisturizing hair conditioners. Humectants are also used in the manufacture of some cigarettes.
Examples of humectants include glycerine, propylene glycol (E 1520) and glyceryl triacetate (E1518). Others can be polyols like sorbitol (E420), xylitol and maltitol (E965), or polymeric polyols like polydextrose (E1200) or natural extracts like quillaia (E999), or lactic acid or urea. Lithium chloride is an excellent humectant.