Biological Effects of High-Frequency Electromagnetic Fields on CNS Function and Neuroimmune Responses: A Systematic Review of In Vitro and In Vivo Experimental Studies.

Background the deployment of fifth-generation (5G) wireless telecommunications infrastructure, incorporating millimeter-wave (mmWave, 24-100 GHz) and sub-6 GHz frequencies, has renewed scientific and public health interest in the potential neurobiological effects of radiofrequency electromagnetic fields (RF-EMF). While extensive research has examined lower-frequency RF-EMF from 2G/3G/4G technologies, the specific effects of mmWave frequencies on CNS cellular biology-including microglial polarization and intracellular calcium signaling-remain less characterized. This systematic review evaluates experimental evidence from in vitro and in vivo studies on the effects of high-frequency EMF (300 MHz-300 GHz) on neuroimmune responses, microglial function, CNS calcium homeostasis, and related outcomes. Methods PubMed, EMBASE, Web of Science, and the EMF-Portal were searched from inception to January 2026 following PRISMA 2020 guidelines. Experimental (in vitro and animal) studies reporting CNS-relevant outcomes after high-frequency RF-EMF exposure were eligible. Exposure must have been within the 300 MHz to 300 GHz range. Quality assessment used adapted OHAT risk-of-bias criteria. A narrative synthesis was conducted; quantitative pooling was performed where three or more studies reported the same outcome. Results forty-one studies met inclusion criteria (see PRISMA Flow Diagram, Fig. 1): 7 in vitro (cell culture), 29 in vivo (rodent model), and 5 reviews/meta-analyses. The detailed characteristics of all included studies are summarized in Table 1. At specific absorption rate (SAR) levels at or below the International Commission on Non-Ionizing Radiation Protection (ICNIRP) general public exposure guidelines (2 W/kg averaged over 10 g), the majority of studies (27/41, 66%) found no statistically significant effects on neuroinflammatory markers, microglial morphology, or calcium signaling. Eleven studies (27%) reported transient, low-magnitude increases in intracellular Ca²⁺ or pro-inflammatory cytokine expression at exposures near or exceeding guideline limits; these effects were not consistently reproducible across independent laboratories. Three studies (7%) reported effects below guideline thresholds that may warrant further investigation. No study identified neuropathological changes (neuronal death, axonal injury) attributable to RF-EMF at guideline-compliant exposures. Conclusions current experimental evidence does not establish that high-frequency RF-EMF at guideline-compliant exposure levels produces significant adverse effects on microglial polarization, CNS calcium homeostasis, or neuroinflammatory responses. Methodological heterogeneity, inadequate dosimetry, and limited independent replication constrain confidence in both positive and negative findings. Standardized, rigorously controlled experimental studies are needed, particularly for mmWave frequencies (> 6 GHz) where data are sparse. Our findings support the current scientific consensus that high-frequency RF-EMF below regulatory limits does not pose a clearly established neurobiological hazard.