## 4 Discussion  
The present study aimed to evaluate how various electromagnetic field (EMF) configurations influence the transdermal delivery and skin retention of salicylic acid, with a particular focus on improving permeability and enabling controlled release. The findings demonstrate that EMFs, especially pulsed and rotating magnetic fields, can serve as promising tools in modulating the skin barrier and transport dynamics of this moderately lipophilic compound. Figure 4: Accumulation of salicylic acid in porcine skin after 8 h of transdermal exposure under different electromagnetic field conditions. Data are expressed as mean \(\pm\) SD (n = 3). Mean \(\pm\) SD, n = 3; \(\alpha\) = 0.05 (mean \(\pm\) SD, n = 3). *—statistically significantly smaller accumulation compared to control. The statistically significant difference was estimated by ANOVA using Tuckey’s test. Among the tested EMF types, pulsed magnetic fields (PMFs) showed the most pronounced enhancement of salicylic acid permeability. The PMF configuration with a 5 s on/off cycle (PMF 5/5 s) led to a nearly two-fold increase in cumulative drug permeation and steady-state flux compared to the control. This effect likely results from transient disruptions in the stratum corneum's barrier function, which enhances passive diffusion and facilitates faster skin penetration. Rotating magnetic fields (RMFs), particularly at 30 Hz and 50 Hz, also significantly improved transdermal delivery. RMFs likely enhance permeation by inducing microfluidic movement and reorganizing the skin's lipid layers, thereby reducing barrier resistance. Interestingly, oscillating magnetic fields (OMFs) exhibited a frequency-dependent effect. While lower frequencies (45-55 Hz) reduced permeation, the OMF at 65 Hz showed a moderate enhancement, suggesting that the optimization of field parameters is critical in achieving a desirable delivery profile. Static magnetic fields (SMFs) displayed highly variable effects, depending on voltage and polarity. Positive polarity SMFs at higher voltages enhanced transdermal flux, whereas negative polarity fields significantly suppressed it. These findings suggest that field orientation and strength significantly influence skin permeability, potentially through interactions with charged species or the alignment of lipid domains. Rotating magnetic fields, 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, 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 boundary layer thinning [13,19,28]. 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]. To enable a more quantitative comparison of these effects, enhancement ratios (ER = JSS,EMF/JS,control) were calculated for each EMF configuration (Table S1, Supplementary Materials). Notably, the PMF 5 s on/5 s off mode produced approximately 1.8-fold higher ER values than the highest OMF setting (65 Hz), supporting the role of time-varying amplitude in enhancing transdermal delivery. Likewise, RMFs at 30 Hz and 50 Hz consistently outperformed amplitude-matched SMF and OMF setups, underscoring the additional contribution of vector rotation to transdermal transport efficiency.