No thermal skin effects at environmental 26 GHz field strengths relevant to 5G deployment.

The deployment of 5G millimeter wave technology at 26 GHz raises questions about potential thermal effects on human tissues. Controlled human studies examining millimeter wave thermal responses remain limited. We investigated the effects of acute 26 GHz exposure on skin temperature in healthy volunteers under controlled laboratory conditions. Thirty-one healthy young adults participated in a triple-blind, randomized, crossover study. Participants underwent genuine 26 GHz exposure (2 V/m at head level, 1 V/m at torso level) and sham exposure, each lasting 26 minutes 30 seconds. Skin temperature was continuously monitored using infrared thermography at five anatomical regions (face, bilateral hand dorsum, bilateral infraclavicular areas) across three experimental phases. No statistically significant thermal effects were detected, with no main effect of exposure condition for any skin region (all p > 0.34). No significant exposure-phase interactions were detected for any measurement (all p > 0.09). Progressive decreases in distal skin temperatures (exceeding 1.5°C, p < 0.0001) occurred independently of exposure condition, reflecting normal thermoregulatory adaptation to seated immobility. Distal-proximal gradient analysis showed no significant difference between conditions (right: p = 0.332; left: p = 0.319), and bilateral comparisons revealed no thermal asymmetry (p = 0.269). These findings provide reassuring evidence that acute 26 GHz exposure at environmental field strengths produces no detectable thermal effects in healthy young adults, at levels substantially below ICNIRP reference limits. However, these results should not be interpreted as a direct validation of those guideline threshold values.