A humectant is a product used to preserve moisture in something. Humectants are used as additives in cosmetics and hair care products, in order to provide a moisturising action in shampoos and conditioners, face creams, and make-up. They are also used in food products such as confectionery to stop them drying out or powdering and keep them chewy rather than crunchy. Chemicals with the same function can also be found in other products such as glues (to keep the glue liquid) and in horticulture.
Humectants tend to be hygroscopic chemicals, i.e. they have the property of absorbing water from the air. Most are derived from sugars or fats. Examples of chemicals used as humectants include glycerol (glycerin) and castor oil, which can be used in both food and cosmetics; lactose and sugar derivatives like isomalt (isomaltitol), lactitol, xylitol, polydextrose, sodium lactate, and sorbitol which are used in foods as sweeteners and humectants; propylene glycol, used in beauty products and formerly in foods; various other glycols, diols, and polyols used in glues, paints, etc.; glycerol triacetate (triacetin), used as an additive in rocket fuels and to coat fresh fruit; and hydrogels which are used to provide water for growing plants.
Conversely, you can also come by anti-humectants, which are used in hair care products to fight the effects of humidity (principally frizziness) and keep hair smooth and pristine. Incidentally, if anyone can work out how to transfer the moisture from frizzy hair to dried-out skin (or cereal bars) a fortune surely awaits them.
The word comes from the Latin humectans, the present participle of humectare (to moisten) from humectus (moist).
This entry is brought to you by Asda Tropical Fruit Breakfast Bars and the following websites:
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The American Heritage Dictionary of the English Language: Fourth Edition. 2000.
http://www.bartleby.com/61/10/H0321000.html
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The Free Dictionary. http://www.thefreedictionary.com/humectant
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Melissa Gagliardi. "Let's get this straight". Courier-Journal. Louisville, Kentucky. 2004.
http://www.courier-journal.com/features/style/2004/style_01252004_hair.html
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"Cool word: Humectant". The Mail Archive.
http://www.mail-archive.com/word@tlk-lists.com/msg00162.html
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"Welcome to the world of additives". Avecia.
http://www.avecia.com/additives/dynamicindex.asp?page=http://www.avecia.com/additives/product_list/humectantgrb2.htm
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Food Additives Guide. MDM.
http://www.mbm.net.au/health/900-1520.htm
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Dermnet. New Zealand Dermatological Society.
http://www.dermnetnz.org/index.html