TECHNOLOGY INNOVATION – Chemical Penetration Enhancers | FORMULARY – Light Lotion | Vol. 2, Iss. 2

Technology Innovation - Chemical Penetration Enhancers – Revisiting the role of Propylene Glycol

Active permeation into the epidermis is crucial for product effectiveness. The key difference between a cosmetic and a drug lies in their target depth of action: cosmetics primarily affect the superficial skin layers up to the dermis, while drugs are designed to penetrate deeper and reach systemic circulation. The role of Chemical Penetration Enhancers (CPEs) remains pivotal for transdermal drug delivery. These compounds interact with the intercellular lipid and protein matrix, facilitating the permeation of active molecules.

Propylene glycol (PG) is one of the most widely used CPEs. It not only enhances the solubility of active ingredients in formulations but also provides skin hydration. Infrared Spectroscopic analysis of skin samples treated with PG reveals its interaction with stratum corneum lipids, altering their arrangement and thereby increasing skin permeability. Similarly, Differential Scanning Calorimetry studies demonstrate PG's affinity for bound water in the skin, as well as its interactions with lipids and proteins. Additionally, PG exhibits a solvent ‘drag’ effect, where the active ingredient is carried deeper into the skin as the solvent penetrates.

At typical concentrations of 1–10%, PG serves as both an effective solvent and a cost-efficient penetration enhancer. However, it’s important to note that PG’s permeation enhancement properties can be influenced by other excipients present in the formulation.

References –

• Williams AC, Barry BW. Penetration enhancers. Adv Drug Deliv Rev. 2004 Mar 27;56(5):603-18. doi: 10.1016/j.addr.2003.10.025.
• Carrer V, Alonso C, Pont M, et al. Effect of propylene glycol on the skin penetration of drugs. Arch Dermatol Res. 2020 Jul;312(5):337-352. doi: 10.1007/s00403-019-02017-5. Epub 2019 Nov 30. PMID: 31786711.
• Tanojo H, Bouwstra JA, Junginger HE et al. Thermal Analysis Studies on Human Skin and Skin Barrier Modulation by Fatty Acids and Propylene Glycol. J Therm Anal Calorimetry 1999, 57, 313–322. doi: 10.1023/A:1010137807610

Formulary - Light Lotion

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