scientific article about alcohol in hair products
We have all heard the advice that it is best to avoid the use of products that contain alcohol, as it can be drying to the hair. This is especially true for those of us with curly hair, which has the tendency to need all the moisture it can get. However, we often get a little baffled; because we see ingredients including the word ‘alcohol’ in many of the products we buy, including those that are labeled as conditioning products. The explanation is a fairly simple one: some alcohols can cause dry, frizzy hair while others can act to condition your hair!
This apparent contradiction in performance is due to the structure of the alcohol. Alcohols are a class of materials defined by certain characteristics. They have a nonpolar carbon chain and a polar hydroxyl group (an oxygen atom bonded to a hydrogen atom) bonded to one of the carbons in the chain (most often at the end of the chain). We’ll look at the various types of alchohols.
This group includes ethanol, SD alcohol, SD alcohol 40, Alcohol denat, Propanol, Propyl alcohol and Isopropyl alcohol.
Due to similarities with water molecules, the very small alcohols (ones with fewer than 3 carbons in the tail) are slightly miscible (capable of mixing) in water, while they can also dissolve oil and other ingredients that are not miscible with water. Thus, one function they can serve is to dissolve polymers or other additives prior to their addition to the aqueous portion of the formula.
These types of alcohols evaporate quickly due to their low molecular weight, and for this reason are often used as an additive to help decrease the time it takes for hair to dry. However, this can create dry, frizzy hair as it may cause the cuticle to be roughened and/or oil and water to be removed from the hair along with the alcohol (remember, these are often use as astringents for our skin for just this reason). Another function of these lower molecular-weight alcohols, particularly ethanol (SD alcohol, SD alcohol 40, Alcohol Denat) is to ensure the proper, even spreading of styling products onto the hair.
This group includes Lauryl alcohol, Cetyl alcohol, Myristyl alcohol, Stearyl alcohol, Cetearyl alcohol and Behenyl alcohol.
These larger alcohols are typically derived from natural sources, and have 12 or more carbons per molecule (typically 12, 14, 16, 18, and 20). This higher amount of carbon content makes these molecules oilier (also referred to as ‘fatty’). For this reason, they are often used as an emollient in skin and haircare products. They give a smooth, soft feeling to the hair shaft by helping the cuticle to lie flat on the surface of the hair. However, if used in excess, fatty alcohols can combine with the natural sebum found on the scalp and form a sticky substance that makes the hair look greasy.
Another function these fatty alcohols typically perform in shampoos and conditioners is as thickeners and as nonionic surfactants and emulsion stabilizers. In fact, a fatty alcohol content of 4-5% is very common for this purpose; especially in products where there is a need to keep the price lower than that of a formula containing an expensive polymer that could achieve similar results.
Benzyl alcohol is a non-volatile alcohol used as a preservative in products. It should not impact the texture or feel of your hair. Propylene glycol is most often used as a humectant, because it has a hydroxyl group at each end of the molecule. This makes it much more hydrophilic (water-loving), so that it can attract and hold water to the hair.
Some alcohols may cause our delicate curly hair to be dried and frizzy, and we do well to avoid those in most cases. However, other alcohols such as cetyl alcohol can help to condition our hair and make it soft and manageable. In general, curlies might want to be cautious of short-chain alcohols, and not so worried about fatty alcohols, benzyl alcohol or proplyene glycol. As with all ingredients, it is always best to use trial and error as a method for determining what gives you the best results.