MECHANISM

Potential hazards associated with RF-EMF depend primarily on frequency, exposure duration, and incident power density (i.e. power per unit area).11 The only consensus mechanism for adverse health effects from exposure to RF frequencies > 5 megahertz (MHz) is bulk tissue heating. RF energy is absorbed by the body and converted to heat at a rate and distribution primarily determined by the oscillating frequency and incident power density of the exposure, along with geometrical considerations (e.g., incident angle, polarization of the energy, body posture and morphology). In contrast, overexposures below 5 MHz may result in painful spark discharges. Unlike with ionizing radiation, cumulative health effects do not occur at RF frequencies (100 kHz - 300 GHz).3

PENETRATION DEPTH

The depth that the energy penetrates the body before being absorbed is a function of RF frequency and physical properties of the tissue (i.e. tissue penetration depth is inversely related to RF frequency). Thus, overexposure injuries will be more “superficial” in nature at higher RF frequencies, and more “whole body” in nature at lower RF frequencies. For example, the penetration depth of a 3 GHz exposure on human skin is approximately 19 mm (with relatively similar values for other tissue types) so that the primary adverse health effect for > 3 GHz overexposures will be skin burns and eye damage.12-15

Between 100 kHz and 3 GHz (i.e. < 3 GHz), however, RF energy can penetrate deeper (i.e. > 19 mm). Potential systemic adverse health effects of overexposure include heat exhaustion and heat stroke, and partial body exposures could result in localized tissue damage due to hyperthermia.

BELOW EXPOSURE LIMITS

Because RF-EMF hazards follow a dose response relationship, adverse health effects should not be expected with doses below the safety limits. Few RF-EMF health effects were documented and characterized below exposure limits.16 In 2020, the U.S. Food and Drug Administration (FDA) concluded “insufficient evidence to support a causal association between RF radiation and tumor formation.”17 The National Toxicology Program has not included RF-EMF radiation in the Report on Carcinogens.18

For effects on testes, one of the most sensitive organs to RF-EMF exposures, Grajewski et al. observed minor semen quality and hormonal change among 12 industrial RF heater operators.19 Yet, a recent meta-analysis of pooled human cross-sectional studies showed no significant association of mobile phone use and decline in sperm quality.20,21

The microwave auditory effect, described by subjects as hearing a “click, buzz, hiss, knock, or chirp” sound from pulsed RF energy, led to the development of the thermoelastic expansion theory.22 A computational model suggested that theoretically, thermal expansion could be induced in the human brain by extremely high-power (> 15 MW/m2), pulsed RF-EMF sufficient to cause neuropathological effects.23,24 These pulses would be less than 50 microseconds in duration so despite the high instantaneous power densities would be well below the safety standard. It has been speculated that this could result in audio vestibular and cognitive symptoms (e.g., ear popping, vertigo, pounding headaches and nausea).25 However, this effect has not been observed in any confirmed human RF exposures nor has a repeatable effect been observed in animal studies.26 There is currently no well-established scientific evidence of a causal relationship between RF-EMF radiation and TBI. This CPG will be updated if such scientific evidence emerges.

ABOVE EXPOSURE LIMITS

The Standard for Military Workplaces includes a 50X safety margin for unrestricted and a 10X safety margin for restricted military environments (Appendix A).3 Additionally, the safety standard is based on the levels required for subtle behavioral change in animals and not on human adverse health effects. As a result, most overexposure incidents may not result in adverse health effects. With increasing dose above the standard, however, the risk and severity of adverse health effect will increase.

RF health effects continue to be investigated under an international EMF project sponsored by the World Health Organization (WHO).27 Most studies were performed using cell or animal models.28-30 These studies provided basic information on biological effects of RF-EMF overexposure, but how to effectively apply the study results to humans are yet to be determined.20 Further epidemiological studies are needed to confirm possible long-term biological effects of RF-EMF exposure to humans.

POTENTIAL ACUTE HEALTH EFFECTS

Overexposure to RF-EMF may result in various acute health effects:

1. Skin heating effects that induce skin burns;
2. Thermal effects that increase body temperature;
3. Electro-stimulatory effects that cause painful nerve impulses; and
4. interaction with medical devices or metallic implants.3,8,22,25,31

Proper medical documentation and prudent RF-EMF incident reporting are essential for proper diagnosis and management of patients with RF-EMF overexposure.

In the U.S. Air Force, most reported cases had no or mild signs/symptoms (see clinical scenarios).10 In the few cases resulting in injury, Erwin et al observed skin burns and profuse sweating were common while other symptoms, such as nausea, were found to be nonspecific to RF-EMF overexposure.10 Heat exhaustion and heat stroke may occur when thermoregulation becomes inefficient at high RF-EMF heating levels.16

The safety standard may not protect Service members with implanted medical devices.3,32 Medical assessment and screening for implanted medical devices (e.g., metallic contraceptive implants, artificial joints, surgical screws, stents, implanted drug infusion pumps, etc.) are vital.

OCULAR INJURIES

High dose RF-EMF radiation has been documented to induce ocular injures in non-human primates and rabbits.33,34 Liu et al. reported a case of bilateral vision loss in human due to optic nerve damage from misuse of a medical device at 90 to 580 kHz RF radiation.35 However, Adibzadeh et al. observed no serious acute ocular injuries in 16 patients undergoing treatment of cancer in the head and neck region by hyperthermia induced by prolonged (60 min) and intense exposure of 434 MHz RF-EMF radiation.36 In general, the presence and extent of eye damage will be frequency and dose dependent and can be substantially mitigated by facial aversion and the blink reflex.37 Because eye damage is possible at sufficiently high doses, comprehensive eye exam is recommended as a part of the initial medical evaluation for patients with ocular or visual complaints.