Heating and pain sensation produced in human skin by millimeter waves: comparison to a simple thermal model

Cutaneous thresholds for thermal pain were measured in 10 human subjects during 3-s exposures at 94 GHz continuous wave microwave energy at intensities up to approximately 1.8 W cm(-2). During each exposure, the temperature increase at the skin's surface was measured by infrared thermography. The mean (+/- s.e.m.) baseline temperature of the skin was 34.0+/-0.2 degrees C. The threshold for pricking pain was 43.9+/-0.7 degrees C, which corresponded to an increase in surface temperature of approximately 9.9 degrees C (from 34.0 degrees C to 43.9 degrees C). The measured increases in surface temperature were in good agreement with a simple thermal model that accounted for heat conduction and for the penetration depth of the microwave energy into tissue. Taken together, these results support the use of the model for predicting thresholds of thermal pain at other millimeter wave (length) frequencies.