Biological effects of low power nonionizing radiation: A narrative review

Background and controlled electromagnetic radiation (EMR) on biological cells and tissues induces thermal, non-thermal, and dielectric property change. After EMR interaction with cells/tissues the resulting signal is used for imaging, bio-molecular response, and photo-biomodulation studies at infrared regime, and for therapeutic use. We attempt to present a review of current literature with a focus to present compilation of published experimental results for each regime viz. microwave (extremely low frequency, ELF to 3 GHz), to cellular communication frequencies (100 KHz to 300 GHz), millimeter wave (300 GHz- 1 THz), and the infra-red band extending up to 461 THz. A unique graphical representation of frequency effects and their relevant significance in detection of direct biological effects, therapeutic applications and biophysical interpretation is presented. A total of seventy research papers from peer-reviewed journals were used to compile a mixture of useful information, all presented in a narrative style. Out of the Journal articles used for this paper, 63 journal articles were published between 2000 to 2020. Physical, biological, and therapeutic mechanisms of thermal, non-thermal and complex dielectric effects of EMR on cells are all explained in relevant sections of this paper. A broad up to date review for the EMR range KHz-NIR (kilohertz to near infra-red) is prepared. Published reports indicate that number of biological cell irradiation impact studies fall off rapidly beyond a few THz EMR, leading to relatively a smaller number of studies in FIR and NIR bands covering most of the thermal effects and microthermal effects, and rotation-vibration effects.