## 4 Discussion
The enhanced transdermal permeability of salicylic acid observed under pulsed and rotating electromagnetic field conditions, in contrast to the more modest effects of static and oscillating fields, may be associated with several biophysical processes that act synergistically to modulate skin barrier properties. Although the precise mechanisms remain incompletely understood and are still under investigation, several plausible hypotheses can be formulated based on prior studies. Pulsed magnetic fields are characterized by high-gradient, time-varying electromagnetic signals that may influence the organization of the stratum corneum lipid matrix. It is postulated that such exposures can lead to transient alterations in membrane fluidity and lipid packing, potentially creating short-lived aqueous channels that enhance passive drug diffusion. While this mechanism has not been definitively demonstrated for salicylic acid, similar increases in permeability have been observed for nonsteroidal anti-inflammatorydrugs (NSAIDs) like ibuprofen and naproxen when exposed to pulsed or modulated EMFs [16; 18; 19; 28]. Rotating magnetic fields (RMFs), on the other hand, appear to enhance drug transport, predominantly through convective phenomena. The continuous change in magnetic vector orientation can generate Lorentz forces in the conductive donor and receptor media, resulting in micro-scale vortices and shear flows. These fluid movements may reduce the effective thickness of the unstirred aqueous boundary layer (UAL), which is a known rate-limiting step in transdermal diffusion. This mechanism is supported by recent experimental data showing enhanced ibuprofen permeation in RMF-exposed systems due to the thinning of the boundary layer [13; 19]. Static magnetic fields (SMFs), particularly those with a negative polarity, may exert a different type of effect--one that does not directly enhance permeation but rather modifies retention. It has been suggested that SMFs could interact with diamagnetic lipid molecules in the stratum corneum, subtly altering their orientation or dynamics, and potentially limiting lateral molecular diffusion. As a result, higher accumulation within skin layers may occur even in the absence of an increased flux across the membrane [16; 19; 28]. These observations suggest that EMF-induced changes in skin permeability are multi-factorial, depending not only on field strength but also on waveform characteristics such as pulse duration or vector rotation. PMFs may promote transient barrier modulation, while RMFs introduce convective enhancement mechanisms. SMFs, in contrast, may affect the mobility and retention profile of the drug within the skin. To enable a direct cross-comparison, enhancement ratios (ER = JSS,EMF/JSS,control) were calculated for each electromagnetic field configuration (Table S1, Supplementary Materials). These ER values revealed two major trends. First, among field types with similar magnetic induction values, pulsed magnetic fields (PMF), especially the 5 s on/5 s off configuration, generated approximately 1.8 times higher enhancement ratios compared to continuous oscillating fields (OMFs at 65 Hz), suggesting that instantaneous amplitude spikes play a critical role in promoting drug permeation. Second, rotating magnetic fields (RMFs) at 30 Hz and 50 Hz consistently outperformed both OMF and SMF setups with comparable field strengths, indicating that dynamic vector rotation adds a direction-dependent enhancement mechanism. These findings collectively suggest that both field intensity peaks and rotational dynamics contribute to modulating transdermal permeability, and that their relative significance depends on waveform characteristics. Skin accumulation data revealed that certain EMF configurations could selectively favor drug retention over permeation, indicating potential for reservoir-type release systems. Notably, SMFs with a negative polarity (\(-5\) V and \(-15\) V) yielded the highest levels of skin-retained salicylic acid, despite poor permeation metrics.