Chemical(s) of the Day: Alcohol
I'll skip right to the conclusion: rubbing alcohol and vodka are not the only kinds of alcohol. Not all alcohols are drying to the skin and hair; some fatty alcohols are actually moisturizing. Now, moving on....
When most of us hear the word 'alcohol', we think wine, beer, or liquor. We may also think of the doctor's office and a little pad soaked with rubbing alcohol used to prep the skin before getting a shot. To a chemist, however, alcohol is 'any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom, which in turn is bound to other hydrogen and/or carbon atoms'. (Remember that to a scientist, the word 'organic' refers to compounds that contain carbon, not 'USDA Organic Certified').
There are also sugar alcohols (like zylitol and sorbitol) that are added to food, and fatty alcohols that act as slip agents, emollients, hydrators, and penetration enhancers (meaning they help the active ingredients in the product you're using penetrate the skin deeply enough to have an effect).
Short-chain Alcohols (the Drying Alcohols)
These alcohols have less than 3 carbons in the tail of their molecules. Examples include ethanol, SD alcohol (the 'SD' stands for 'specially denatured - more on that in a minute), SD alcohol 40/denatured alcohol, propanol, and isopropyl alcohol. They evaporate quickly but can also be drying to hair and skin. These kinds of alcohols are usually found in hair sprays, hair gels, and hand sanitizers because they evaporate so quickly.
So what's the SD mean? It means something poisonous, bad tasting, foul smelling or nauseating has been added to the ethyl alcohol to discourage recreational consumption. (Side note: There's a fascinating history about the addition of poisons to alcohol to discourage the consumption of paint thinners and other industrial solvents during Prohibition. Watch it here: https://www.pbs.org/wgbh/americanexperience/films/poisoners/) What role did the U.S. government play? http://time.com/3665643/deadly-drinking/)
Long-chain Alcohols (the Fatty Alcohols)
These alcohols have a chain of more than 12 carbon atoms per molecule. These alcohols lubricate, hydrate, and can provide slip, gloss, and softness to the hair. Examples include lauryl alcohol, cetyl alcohol, myristyl alcohol, stearyl alcohol, and cetearyl alcohol.
Fatty alcohols in skincare products can be irritating for very sensitive skin, and there is some evidence that certain fatty alcohols can be comedogenic (meaning they can clog pores) and exacerbate acne breakouts.
How Come There are Alcohols on the Ingredient List of this Product Labeled 'Alcohol-Free'?
According to the FDA, the term "alcohol," used by itself, refers to ethyl alcohol. Cosmetic products, including those labeled "alcohol free," may contain other alcohols, such as cetyl, stearyl, cetearyl, or lanolin alcohol. As was stated earlier, these are known as fatty alcohols,
and their effects on the skin are quite different from those of ethyl alcohol. (Isopropyl alcohol, which some consumers may think of as drying the skin, is rarely used in cosmetics).
SUGAR ALCOHOLS
Sugar alcohols are actually "polyols". Part of their chemical structure resembles sugar, and part of it resembles alcohol—hence the name. Examples include maltitol, sorbitol, isomalt, and xylitol. Sugar alcohols occur naturally in plants, but some are man-made and are added to processed foods. Many foods labeled "sugar free" or "no sugar added" have sugar alcohols in them. Sugar alcohols don't cause cavities, which is why they're used in sugar-free gums and mouthwashes. Sugar alcohols can create a cooling sensation when used in large amounts, which works well with minty flavors. You may see sugar alcohols as ingredients in many lower-calorie and sugar-free foods like energy bars, ice cream, pudding, frosting, cakes, cookies, candies, and jams. (And no, sugar alcohols cannot make you drunk!)
RESOURCES
https://www.futurederm.com/why-alcohol-in-skin-care-is-safe-despite-what-paula-begoun-says/
https://www.fda.gov/Cosmetics/Labeling/Claims/ucm2005201.htm
https://consumerist.com/2016/03/23/why-does-my-alcohol-free-product-list-alcohol-as-an-ingredient/