Transdermal delivery materials for polyphenols in whitening and anti-aging applications

Polyphenols have emerged as promising agents in the field of skin whitening and anti-aging due to their natural origin, excellent biocompatibility, and ability to modulate multiple biological pathways. Mechanistically, polyphenols inhibit melanin production through modulation of the tyrosinase (TYR) and microphthalmia-associated transcription factor (MITF) signaling pathways, and preserve collagen structure and dermal integrity by suppressing ultraviolet (UV)-induced reactive oxygen species (ROS) generation and matrix metalloproteinases (MMPs) expression. Unlike conventional agents such as hydroquinone, kojic acid, and tretinoin, which easily cause skin irritation and allergy, polyphenols are associated with fewer side effects, broader biological activities, and better suitability for long-term transdermal use. Despite these advantages, the application of polyphenols in cosmetics is hindered by intrinsic limitations, including poor aqueous solubility, low chemical stability under physiological conditions, and inadequate skin permeability, which significantly restrict its bioavailability and cosmetic performance. To address these issues, researchers have constructed a variety of delivery systems through exploiting the merits of delivery materials, which not only enhance the physicochemical properties of polyphenols, such as solubility, stability, and controlled release, but also improve the interaction with skin physiological features including skin barrier modulation, skin hydration, skin occlusion, and skin adhesion. These properties can increase skin retention and penetration for more precise delivery and significantly improve whitening and anti-aging effects. In this review, we first give a brief introduction to polyphenols for whitening and anti-aging applications. We then focus on the latest applications of three types of materials, namely phospholipids, neutral esters, and polymers, in transdermal delivery systems of polyphenols for skin whitening and anti-aging. Lastly, we discuss the important roles of delivery materials in improving transdermal delivery performance to provide valuable insights into the design and development of more effective delivery systems.