ABSTRACT Background Transdermal drug delivery (TDD) is an established pharmaceutical route for systemic therapeutic delivery, yet the umbilical skin - the specific site employed in the ancient Ayurvedic practice of Nabhi Chikitsa (navel therapy) - has received minimal dedicated pharmacological investigation compared to conventional transdermal sites such as the arm, abdomen, or back. This review critically appraises the anatomical, histological, embryological, and pharmacokinetic evidence bearing on umbilical skin as a distinct and pharmacologically advantaged locus for percutaneous drug absorption relative to standard non-genital transdermal sites. Methods A narrative review of literature published between 1980 and 2024 was conducted using PubMed, Scopus, Web of Science, and Google Scholar. Search terms included: umbilical transdermal absorption, navel skin permeation, periumbilical drug delivery, Nabhi Chikitsa pharmacokinetics, umbilical histology, stratum corneum thickness, skin lipid composition, and herbal transdermal formulation. A total of 96 peer-reviewed articles and 12 pharmacopoeial references met inclusion criteria and were synthesised. Results The umbilical skin exhibits several physiological characteristics that collectively favour enhanced percutaneous absorption relative to standard transdermal sites: (1) a measurably thinner stratum corneum (4-8 cell layers vs. 15-20 layers at standard abdominal skin), supported by direct histological studies using umbilical biopsies; (2) an elevated ratio of intercellular lipids to keratin, facilitating passive diffusion of lipophilic molecules; (3) proximity of vestigial umbilical vascular structures (ligamentum teres hepatis, medial umbilical ligaments), the pharmacokinetic relevance of which remains a testable but currently unconfirmed hypothesis; (4) a uniquely dense periumbilical autonomic innervation with direct connections to the celiac plexus at T10-T12; and (5) a moist, occluded microenvironment within the umbilical cavity that naturally enhances skin hydration and drug permeability. Available pharmacokinetic and ex vivo studies, while limited in number, consistently demonstrate 2-2.6-fold enhancement in transdermal flux at the umbilical compared to standard abdominal and forearm sites for lipid-soluble compounds. Conclusion The umbilical site presents a pharmacologically plausible and scientifically distinct route for transdermal delivery, warranting systematic ex vivo permeation studies, in vivo pharmacokinetic characterisation, and regulatory-grade safety profiling. The absence of dedicated research on umbilical transdermal pharmacokinetics represents a major and addressable gap in pharmaceutical sciences and integrative medicine. Definitive comparative superiority over other established transdermal sites requires adequately powered prospective pharmacokinetic studies.
Warty et al. (Fri,) studied this question.