Topical Benefits of Propylene Glycol
- Propylene Glycol
Propylene glycol is a synthetic water-soluble liquid that is capable of absorbing water. Propylene glycol is used as an anti-freezing agent by the pharmaceutical, chemical, and food industries. The US Food and Drug Administration (FDA) has declared propylene glycol a safe compound to be used as a food additive. Propylene is tasteless and odorless. This compound is also known as methyl glycol, trimethyl glycol, 1, 2-propanediol, and 1, 2-dihydroxypropane.
Propylene glycol is produced synthetically; however, it can be derived from natural products including Arabidopsis thaliana and Vitis vinifera. (Information, 2022)
In addition to its use in automotive industries, propylene glycol is also used in the manufacturing of cosmetic formulations. It serves as a viscosity-decreasing agent, fragrance ingredient, and skin-conditioning agent. Propylene glycol is also used in hair sprays, however, the aerosol particles are not respirable and usually settle in the nasopharyngeal regions. The non-cosmetic uses of propylene glycol include both direct and indirect food additives. Propylene glycol is also added to the oral and topical drug formulations as an inactive ingredient. (Fiume et al., 2012)
- Topical Benefits of Propylene Glycol
2.1 Antimicrobial Properties of Propylene Glycol
Propylene glycol and related compounds demonstrate antimicrobial properties against Escherichia coli, Staphylococcus aureus, Candida albicans, Streptococcus pyogenes A, Staphylococcus epidermidis, and Streptococcus mitis. (Kinnunen & Koskela, 1991)
2.2 Propylene Glycol as a Skin Moisturizer
Propylene glycol is integral to all the three constituents of a skin moisturizer – emollients, humectants, and occlusives. As an emollient, propylene glycol deposits between the desquamating corneocytes and makes the skin appear soft and smooth. The moisturizers form a protective barrier over the skin which minimizes the transepidermal water loss (TEWL) and maintains the skin hydration. The hydration effect of moisturizers also improves the dehydration lines, particularly around the eyes. An intact and healthy skin barrier prevents and manages xerosis, a dermatologic condition characterized by abnormal desquamation of the corneocytes owing to the reduced water content of the skin. Propylene glycol also functions as a humectant, attracting water molecules and retaining moisture in the skin. As a humectant, propylene glycol withdraws the water molecules from the air. Both body and face moisturizers contain propylene glycol in addition to other essential ingredients. (Draelos, 2018)
2.3 Propylene Glycol and Skin Barrier Repair
The humectant properties of propylene glycol are responsible for restoring the skin barrier. The humectants absorb water and the resultant water flux serves as a stimulus to repairing the skin barrier. The partial occlusive effect of propylene glycol helps create an artificial film over the skin surface to maintain the hydration of the stratum corneum until the skin barrier is repaired. Restoring the skin permeability barrier is integral to healthy skin. This is also important for the prevention and management of inflammatory skin conditions. (Panzuti et al., 2020)
2.4 Propylene Glycol Enhances Skin Penetration
Topical application and penetrability of pharmacologic formulations through the skin can be enhanced using propylene glycol. The combination of propylene glycol, alcohols, and long-chain fatty acids can significantly improve the penetration of pharmacologic formulations such as acyclovir, which otherwise have poor permeability through the skin. (Cooper et al., 1985)
2.4 Propylene Glycol for Acne
Propylene glycol is found in moisturizers with and without anti-acne medications. Moisturizers improve the efficacy, soothe the skin, and reduce dryness caused by anti-acne formulations such as retinoids and salicylic acid. Since humectants increase skin hydration and TEWL simultaneously, the moisturizers also contain occlusive agents that help trap skin moisture. (Chularojanamontri et al., 2014)
- Safety Profile of Propylene Glycol
Propylene glycol does not exhibit dermal, developmental, and reproductive toxicities. The compound is not carcinogenic and genotoxic. Topical application of propylene causes no or very mild skin irritation. Therefore, the use of propylene glycol in cosmetic products is considered relatively safe. Propylene glycol does not cause skin sensitization and does not demonstrate inhalation toxicity. (Fiume et al., 2012)
Chularojanamontri, L., Tuchinda, P., Kulthanan, K., & Pongparit, K. (2014). Moisturizers for Acne: What are their Constituents? J Clin Aesthet Dermatol, 7(5), 36-44.
Cooper, E. R., Merritt, E. W., & Smith, R. L. (1985). Effect of fatty acids and alcohols on the penetration of acyclovir across human skin in vitro. Journal of pharmaceutical sciences, 74(6), 688-689.
Draelos, Z. D. (2018). The science behind skin care: moisturizers. Journal of cosmetic dermatology, 17(2), 138-144.
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. (2012). Safety assessment of propylene glycol, tripropylene glycol, and PPGs as used in cosmetics. International journal of toxicology, 31(5_suppl), 245S-260S.
Information, N. C. f. B. (2022). PubChem Compound Summary for CID 1030, Propylene glycol. https://pubchem.ncbi.nlm.nih.gov/compound/Propylene-glycol#section=Biochemical-Reactions
Kinnunen, T., & Koskela, M. (1991). Antibacterial and antifungal properties of propylene glycol, hexylene glycol, and 1, 3-butylene glycol in vitro. Acta dermato-venereologica, 71(2), 148-150.
Panzuti, P., Videmont, E., Fantini, O., Fardouet, L., Noel, G., Cappelle, J., & Pin, D. (2020). A moisturizer formulated with glycerol and propylene glycol accelerates the recovery of skin barrier function after experimental disruption in dogs. Veterinary dermatology, 31(5), 344-e389.