Scientists are still investigating the effects of low-level exposure to microwave radiation, but they know that it can heat body tissue in the same way it heats your leftover spanakopita. The FDA requires that microwaves on the market today
limit the amount of radiation they can leak in their lifetime to 5 milliwatts per square centimeter at roughly 2 inches away from the oven. That's below levels that have been shown to harm humans, according to the Center for Devices and Radiological Health, the unit of the FDA that regulates microwave oven safety. O'Connor reports that manufacturers are also required to line oven doors with a metal mesh that prevents waves from escaping, as well as a latch that halts wave-making when the door pops open. He adds that because radiation levels drop with distance, the levels 2 feet away are about one hundredth the amount at 2 inches.
Rest easy while reheating:
Unless your appliance is ancient or the door is broken, it's safe to check if the cheese on your pizza is bubbling while standing an arm's length away.
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