Short note: Microwave radiation hazards

Microwave radiation (300 MHz–300 GHz) is non-ionising, but it becomes hazardous when the body absorbs more energy than it can remove as heat.

How it becomes hazardous:

1. Microwaves penetrate tissue and make polar water molecules rotate and ions move; the energy turns into heat (dielectric heating).
2. The rate of absorption is the SAR = σ|E|²/ρ (W/kg). Above about 4 W/kg whole body, core temperature rises by about 1 °C.
3. Tissues with poor blood circulation cannot remove heat: the eye lens (cataract) and testes (reduced sperm count) are most at risk. Burns may occur at high power density.
4. Penetration depends on frequency: lower microwave frequencies heat deep tissues (no warning from skin sensors), higher frequencies heat the skin.
5. Possible non-thermal effects: headache, fatigue, sleep and nervous system effects (not fully established).
6. Indirect hazards: interference with pacemakers, ignition of fuel and explosives.

Limits: ICNIRP/IEEE limit whole-body SAR to 0.08 W/kg for the public and 0.4 W/kg for workers; microwave ovens must leak less than 5 mW/cm² at 5 cm (US FDA).