Cross-scale physical-biological coupling of terahertz radiation with skin: implications for dermatological science...

Terahertz (THz) technology holds significant promise for dermatological biomedicine owing to its non-ionizing nature and high sensitivity to polar water molecules. A fundamental understanding of THz-skin interactions is essential for advancing both basic research and clinical translation. This paper first delineates the electromagnetic transmission characteristics of THz radiation in human skin. Specifically, we analyze THz propagation across five key aspects: the dielectric properties and electromagnetic modeling of skin layers, absorption-dominant attenuation in multilayer tissues, localized field modulation by skin microstructures, energy deposition profiles, and the dynamic influence of physiological states on transmission. We further review the multiscale biological effects of THz exposure, spanning from molecular and organelle regulation at the subcellular level to macroscopic physiological and pathological responsesin vivo. The roles of radiation dose, waveform, and exposure duration in shaping these spatiotemporal outcomes are clarified. Crucially, we elucidate the cross-scale physical-biological coupling mechanisms underlying these effects. These include indirect transduction networks mediated by water molecules, direct resonance and strong-field mechanical perturbations of biomacromolecules, organelle-specific targeting that reprograms energy metabolism, and response heterogeneity arising from the interplay between physical field strength and cellular state. Finally, we evaluate potential dermatological applications-such as targeted intervention in cutaneous tumors, enhancement of transdermal drug delivery, and neuromodulation of pain and pruritus-and identify core bottlenecks impeding clinical adoption. This work offers a robust theoretical framework and scientific reference for mechanistic studies, experimental design, and the translation of THz technology in dermatology.