So many clients ask about microwaves, so I thought I’d share what I’ve learned about them and their safety.

Microwaves have been regulated and certified for safety by the Food and Drug Administration since 1971 and most American homes have a microwave oven. But are they safe? Do they alter your food? Are they safe to operate in your home?

How Microwave Ovens Work

Microwave ovens use electromagnetic radiation to heat and cook foods. Within the oven, an electron tube, called a magnetron, produces short radio waves that travel 186,000 miles per second, called microwaves. They bounce around off the metal interior walls of the microwave oven like a mirror and strike the objects contained in the interior compartment.

Microwaves are fairly low frequency, about 2,450 megahertz, making them non-ionizing, that is, they have enough energy to cause atoms to vibrate, but not enough to knock electrons out of atoms, such as the case with alpha-, beta-, or gamma-particles, or x-rays. In fact, microwaves are lower in energy than electromagnetic waves emitted from television remote controls, laser printers, or even lightbulbs. The difference between microwave radiation and infrared remotes, printers, or lightbulbs, is that microwaves are longer and can penetrate deeper into an object than the other shorter, faster electromagnetic waves, thus causing interior heating rather than just exterior. As wavelength decreases, frequency and energy increase.

Inductiveload, NASA, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons

When microwaves penetrate food, they cause water molecules within to vibrate, creating heat. This is why foods with higher water content cook faster than lower hydrated foods in the microwave oven. On an electromagnetic scale, microwaves are fairly low frequency, possessing only enough energy to penetrate just an inch or so into foods. Thus, microwaved food first heats on the outside through radiated waves and these hot areas cook further inside the food through conduction. Microwaves do pass through objects without water, such as glass, paper, ceramic, and plastic containers, until they hit more dense food items.

Research Findings on Microwave Safety

Let’s look at how microwaving affects exposed food, whether microwaves destroy food pathogens, potential exposure to microwave radiation, and thermal burns from microwaved foods.

How Microwaving Effects Food

Much research has been done on the nutritional quality of foods that have been microwaved versus other conventional cooking techniques. Vitamins and minerals are retained in microwaved foods, including B vitamins and retinol. Dried legumes cooked in the microwave have shown improved nutritional quality and increased digestibility over conventional means. Small batch blanching of vegetables in the microwave are shown to retain their nutrient value, color, and quality. These were primarily noted in plant-based foods. Meat, on the other hand, generates more harmful products of cholesterol oxidation when microwaved.

Pathogen Resistance

Microwaved food heats unevenly, causing concern over the risk of food-borne pathogens when cooking raw foods in the microwave. Many pathogens are found in animal-based foods after microwaving. Poultry cooked in microwaves consistently leaves living bacteria, specifically listeria and salmonella, clostridium, and staphylococcus aureus, especially when roasting whole, although cooking poultry pieces, such as drumsticks or wings, adequately destroys listeria. E. coli is effectively destroyed with microwave cooking of raw ground beef and fish, although clostridium in fish can survive microwave cooking.

Research shows microwave treatment of contaminated herbs, spices, and vegetables effectively eliminates pathogens.

Radiation Exposure

Many people express concern about radiation leaking from microwaves. Studies show that the small amount of radiation generally leaked from a microwave is not enough to cause human harm, including those with implantable cardiac pacemakers. Generally, leakage occurs from defective door locks, hinges, and defective door seals, so make sure your microwave is in good working order to prevent leaks!

Burn Injuries

Burns are the most common injuries from microwaving food. Some foods, such as eggs, potatoes, and winter squash can trap pressurized steam within and cause burns, especially to the face and eyes.

Not an Easter goes by in the Thompson family where we don’t recall the famous exploding Easter egg!

We got our first microwave in the late 1970s. My grandmother really wanted a warmed hard-boiled egg for Easter breakfast, so we peeled an Easter egg and popped it on a plate in our new microwave to warm it up. Everyone giggled at the sight of Grandma Grace’s warmed egg wiggling all over her plate when it was brought to the table from the microwave. While the vibrating hard-boiled egg dancing around the plate was adorable, the entire family sitting around the table utterly shocked when they found themselves covered with hot, pulverized egg when it exploded with a BANG when Grandma stuck it with her fork for eating! Fortunately Grandma was wearing glasses and didn’t burn her eyes, but we and the entire dining room were all covered with yellow hard-boiled egg.

Don’t heat baby formula or breast milk in the microwave due to the potential for significant scald burns in infants, even when the bottle appears cool to the touch.

Best Practices for Using Your Microwave Safely

Here are some recommendations for safe microwave oven use:

• Keep foods small enough to allow adequate energy penetration for cooking.

• Stir often. This allows for thorough and adequate cooking throughout the food product to destroy any harmful pathogens.

• Don’t ever warm hard-boiled eggs or liquids for babies in a microwave due to their propensity to cause thermal burn injuries.

• Pierce raw whole potatoes and winter squash several times with a fork or cut a shallow X with a knife prior to cooking in the microwave to prevent steam entrapment and explosion potential.

• Use and clean your microwave gently and appropriately to reduce risk of microwave energy escaping the unit, and replace it if it’s worn or damaged.

In Summary

Are microwaves safe? Yes.

Do they alter your foods? Not if cooking plant-based foods, but yes if cooking cholesterol-containing animal products.

Are they safe to operate in your home? Yes, as long as the appliance is maintained and used appropriately.