Last Updated on December 2, 2022 by Verna Meachum
Propylene glycol in hair products is a topic that has been hotly debated in recent years. Some argue that propylene glycol is harmful to the hair, while others feel that it is beneficial and helps to promote healthy, shiny hair.
At first glance, propylene glycol may seem like a chemical that is best avoided in hair care products.
However, there is also a growing body of research that suggests propylene glycol may be beneficial for hair.
So which is it: good or bad? We’ll answer that question in a bit. Let’s first look into what it actually is.
What is Propylene Glycol?
Propylene glycol is a chemical compound that is clear, viscous, and strongly hygroscopic liquid. It is dihydric alcohol and is a close associate with glycerin belonging to the same class of chemical compounds.
Propylene glycol is water miscible (can mix with water in all ratios), and commonly used in skin and hair care formulations. It is a multifunctional chemical compound that is added to perform multiple jobs.
Due to its hygroscopic nature, it works as a humectant to impart water molecules to hair and skin surface. It is cost-effective and shows excellent safety and toxicity record for its topical applications in personal care formulations.
Because of its multi-functionality, cost-effectiveness, and ease of formulation, propylene glycol is frequently used in shampoos, conditioners, masks, and hair styling products.
The chemical structure shows the presence of hydroxyl groups attached propane backbone. Its hydrophilic nature makes it highly water-miscible (in simple words water soluble).
Chemical facts about propylene glycol
Propylene glycol is a small molecule with two alcohol groups (-OH). It is also known as 1,2 propanediol.
Polypropylene is a man-made product that comes from the hydration of propylene oxide. Propylene oxide, in turn, is created from petroleum products.
- It is non-toxic in nature and can be easily absorbed by the skin.
- Although propylene glycol has been widely used in hair products for many years, there remains a lot of debate over whether or not it
- It is water-soluble.
- Some experts claim that propylene glycol helps to add moisture, smoothness, and shine.
- It is synthetic.
- It is colorless and odorless.
Is It Good Or Bad?
The truth is that propylene glycol can be beneficial in certain situations. For example, if you have very dry or damaged hair, using propylene glycol-containing products may help to improve the overall health of your hair and make it look shinier, softer, and more vibrant.
However, if you have sensitive or delicate hair that is prone to damage, propylene glycol may not be the best choice for you.
Some users may experience skin irritation from propylene glycol. Reactions such as redness, burning, itching, flaking or feeling dry or tender could occur.
Propylene Glycol in Hair Care Formulations
Propylene glycol works as a humectant and moisturizing agent. It attracts water molecules from the air and delivers them to the hair shaft or scalp cells.2 It also keeps the product stable and does not let it dry out.
Propylene glycol is also added as a solvent in hair coloring and styling formulations. It dissolves dyes and pigments and facilitates their incorporation into the formulation.
Moreover, it works as an anti-freezing, de-icing and plasticizing agent for emulsion products, improving product aesthetic and stability over a wide temperature range.
Do not worry about the term antifreeze or the chemical, propylene glycol. It is safe at low concentrations when used in beauty products.
Its effect on hair quality
Propylene glycol is a moisturizing agent, and being a humectant it demonstrates an ability to attract water molecules and bind them. With two hydroxyl groups attached, it shows excellent water–binding ability.
Hydroxyl groups form hydrogen bonding with water molecules. This highlights its beneficial impact in boosting hair moisture content. It works to address hair and scalp dryness, minimize frizz, and combat hair brittle fibers.
Did you know that propylene glycol is an alcohol? It’s easy for consumers to assume that all alcohols are drying agents, but this isn’t always the case. All alcohols are not the same. The physical and chemical properties of a chemical compound depend upon its chemical structure.
Propylene glycol is not drying alcohol. It does not evaporate, and more importantly does not form a film on the hair shaft.
As mentioned earlier, it also does not leave any tacky feel at all. This makes propylene glycol a suitable moisturizing agent for fine curly hair fibers.
Propylene Glycol Build Up
Propylene glycol does not form a rigid layer on the skin or hair surface. It is highly water soluble (miscible), and thus rinses off easily during washing.
Furthermore, it is a small molecule and only attaches to hair proteins via weak hydrogen bonding. However, hydrogen bonds are easily broken with water during washing.
No scientific report exists that describes propylene glycol build up.
Safety & Toxicity
Propylene glycol has been used in skin and hair care products for years. The Personal Care Products Council under Cosmetics Ingredient Review (CIR) published a safety assessment of propylene glycol in International Journal of Toxicology.3-4
The panel concluded propylene glycol is safe under current usage limits and does not pose any discomfort to scalp skin or hair.
In conclusion, propylene glycol is safe for topical applications only. This does not include oral or intravenous usage.
1. Ullmann’s Encyclopedia of Industrial Chemistry. John Wiley & Sons: 2003.
2. Leyden, J. J.; Rawlings, A. V., Skin Moisturization. CRC Press: 2002.
3. Fiume, M. M.; Bergfeld, W. F.; Belsito, D. V.; Hill, R. A.; Klaassen, C. D.; Liebler, D.; Marks Jr, J. G.; Shank, R. C.; Slaga, T. J.; Snyder, P. W., Safety assessment of propylene glycol, tripropylene glycol, and PPGs as used in cosmetics. International journal of toxicology 2012, 31 (5_suppl), 245S-260S.
4. Fowles, J. R.; Banton, M. I.; Pottenger, L. H., A toxicological review of the propylene glycols. Critical reviews in toxicology 2013, 43 (4), 363-390.