Are Microwave Ovens Bad for You? History, How They Work, Use Around the World, Safety, Nutrition (vs. Boiling and Stir-Frying), the “Microwave Cover” Claim, and How to Use and Choose One

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Warming rice, warming frozen food, prepping vegetables. In Japan, almost every home has a microwave oven.

At the same time, you often hear things like “microwaving destroys nutrients,” “electromagnetic waves stay in the food,” “eating microwaved food changes your blood,” and “some countries have banned them.” You may also see products described as “nutrients don’t drop if you use a microwave cover.”

In this article, we check the following against national statistics, laws, official sources and studies:

• When, where and how was the microwave oven invented?
• How does it heat food?
• How widely is it used around the world, and which country has the highest ownership?
• Do attitudes differ between Japan and other countries?
• Is the microwave oven safe? Is there any harm in eating microwaved food over and over?
• What happens to nutrients? How does it compare with boiling, grilling and stir-frying (gas flame or open fire)?
• Is it true that “nutrients don’t drop if you use a microwave cover”?
• How to use it well, what not to do, power costs, and how to choose one

For cookware materials, see our articles on Teflon-coated cookware and aluminum products and food.

Conclusions

• The microwave oven came from a radar component (the magnetron). Spencer of Raytheon in the US filed a patent in October 1945. In Japan, Toshiba completed the first unit in 1959, and Sharp began mass production in 1962. The “chin” (ding) sound is said to have been chosen by a Sharp developer from the sound of a bicycle bell
• Food heats because “water molecules try to turn to follow the direction of the microwaves.” The frequency (2,450 MHz) is set by Japan’s Radio Act. The explanation “2.45 GHz is the resonant frequency of water” is wrong
• Household ownership in Japan is 97.8% (2014, households of two or more people). The US is also 96.1% (2020); in both countries almost every home has one. By contrast, Germany is 72.2% (2023) and Italy is 53.0% (2018), which is lower. However, survey years and counting methods differ by country, so there is no statistic that can name a “world No. 1”
• Both Japan and the US set a limit on microwave leakage (5 mW/cm² or less at 5 cm from the surface). Measured in practice, leakage was about 1% of the limit (German Federal Office for Radiation Protection). No microwaves or radioactivity remain in food (US FDA and others)
• The accidents that really are common come from “heat” and “fire,” not microwaves. The National Consumer Affairs Center of Japan (NCAC) receives 80 to 100 consultations a year about microwave oven accidents. The causes include frozen food, dirt inside the oven, eggs and sweet potatoes
• No study has shown that eating microwaved food over time causes disease. The often-cited study claiming “blood changes” (Switzerland, 1992) examined only 8 people and was published in a journal without peer review. However, there are studies showing that heating plastic containers makes chemicals and very small plastic particles more likely to be released
• Nutrients are not lost because “it is a microwave oven.” They decrease because they dissolve into water and because heat breaks them down. Calculated from the Standard Tables of Food Composition in Japan, broccoli keeps 44% of its vitamin C when boiled and 91% when microwaved. However, for some foods, such as sweet corn, more remains when boiled
• “Microwave covers eliminate the loss of nutrients” cannot be claimed. We found no study comparing only with and without a cover. Even in microwave cooking without water, vitamin C and folate decrease

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How was the microwave oven invented?

It came from a radar component (US)

The heart of a microwave oven is a vacuum tube called a “magnetron.” It was originally used during World War II to generate radar waves.

Percy Spencer, an engineer at Raytheon in the US, is said to have noticed that a sweet in his pocket had melted while he stood near a magnetron. He then tried popcorn and an egg (American Physical Society, National Inventors Hall of Fame).

• The kind of sweet is unclear. It is often said to be a “chocolate bar,” but his grandson says it was a peanut sweet he carried to give to squirrels
• The patent was filed on October 8, 1945, and granted on January 24, 1950 (US Patent 2,495,429, “Method of Treating Foodstuffs”). Some sources give the discovery as “1946,” but that does not match the patent filing date
• The patent text compares cooking one egg at 2 kW·seconds (versus 36 kW·seconds with earlier methods)

The first product, the “Radarange,” came out in 1947. It was about 1.8 m tall, weighed about 340 kg and cost about $5,000, and was for commercial use such as restaurants. A model small enough for a home kitchen was released in 1967 by Amana (a Raytheon subsidiary) at $495 (IEEE Spectrum, Smithsonian Magazine).

In Japan, Toshiba and Sharp

Both Toshiba and Sharp claim to be “Japan’s first.” Toshiba was first to complete and release a unit; Sharp was first to mass-produce one. Some sources call the turntable a “world first,” but Sharp’s official description says “Japan’s first.”

The “chin” sound came from a bicycle bell

People who used the Sharp R-10 said things like “I didn’t notice it was done and the food got cold,” and the developer is said to have visited bicycle shops and compared bell sounds to choose a sound to signal the end (Kaden Watch’s Sharp company history series). “Chin suru” (to “ding” something) is even listed in dictionaries as “to heat in a microwave oven (slang).”

How a microwave oven works

1. The magnetron emits microwaves (a type of radio wave) at a frequency of 2,450 MHz (2.45 GHz)
2. The microwaves bounce off the metal walls, spread through the cavity and enter the food
3. The water molecules in food have an uneven distribution of positive and negative charge. The electric field of the microwaves switches direction about 2.45 billion times per second, so water molecules try to rotate to follow it
4. The rotation lags slightly behind the electric field, and that energy becomes heat (dielectric heating)

An explanation often used is “water molecules rub against each other and warm up from friction.” Encyclopedias word it similarly, but strictly speaking the heat comes from “the lag as molecules try to rotate (dielectric loss)”; friction is an analogy.

People also say “a microwave oven heats from the inside.” In fact, everything within the depth the microwaves reach (about a few centimeters) heats at the same time, and heat then spreads from there to the center of a large piece of food (NITE, explanation from London South Bank University).

Why 2.45 GHz?

You may see the explanation “2.45 GHz is the resonant frequency of water,” but this is wrong. The frequency at which liquid water absorbs microwaves most strongly changes with temperature: about 10 GHz at 0°C and about 20 GHz at room temperature. 2.45 GHz was chosen so that the waves are not all absorbed at the surface and reach deep into the food (explanation by Chaplin of London South Bank University).

The band around 2,450 MHz (2,400–2,500 MHz) is internationally allocated as the “ISM band” (industrial, scientific and medical use). Wi-Fi (the 2.4 GHz band) and Bluetooth use the same band. This is why Wi-Fi can become unstable while a microwave oven is running, and manufacturers recommend moving the router away from the microwave oven or switching to the 5 GHz band.

Why frozen food is slow to thaw and why metal sparks

• Ice absorbs almost no microwaves. The molecules in ice are locked tightly by hydrogen bonds and rotate poorly (Tanaka & Sato 2007). This is why thawing frozen food takes time and why only the parts that have melted may start to boil
• Salty food heats more easily. Dissolved ions move and collide with water molecules (same source)
• Metal reflects microwaves, and electric charge collects at sharp points and thin spots, causing sparks. You cannot use aluminum foil, metal containers, or dishes with gold or silver patterns (Hitachi)

What does the law require?

Legally, a microwave oven in Japan is “high-frequency utilization equipment,” and installing one would normally require government permission. Because manufacturers obtain the government’s “type verification,” households can use them without a permit (Article 46-7 of the Radio Act Enforcement Regulations).

Microwave-only models, microwave ovens with oven, and steam combination ovens

NITE explains that “microwave heating” warms food from the inside with electromagnetic waves, while “heater heating” cooks it from the outside with heat from a heater. A combination oven has both in one unit. We cover how to choose in Recommended microwave ovens and how to choose.

Microwave ovens around the world: Which country has the highest ownership?

Japan: Passed half in 1987, now almost every household

In the Cabinet Office survey, ownership among Japanese households (two or more people) was 2.1% in 1970. It passed half for the first time in 1987 at 52.2% and reached 96.5% in 2004. The Cabinet Office stopped asking about microwave ovens after that year; the later Ministry of Internal Affairs and Communications (MIC) survey gives 97.5% in 2009 and 97.8% in 2014. The 97.8% in 2014 was the fifth highest, after refrigerators, washing machines, TVs and vacuum cleaners. For one-person households it is 92.4%.

Ownership by country

We cannot name the “country with the highest ownership.” We found no official international statistic that lines countries up on the same basis. As far as we could verify, Japan and the US are in the highest group, with almost every household owning one. Note, however, that Japan’s 97.8% is for households of two or more people and drops slightly when one-person households are included.

What we can say clearly is that there is a large gap even within Europe. In Germany, more households own a dishwasher (78.0%) than a microwave oven (72.2%), and in Italy only about half of homes have one. In urban China, ownership differed widely by region: 98 units per 100 households in Shanghai versus 37 in Heilongjiang Province (2011). A research firm gives a figure of “less than 4%” for India, but we could not verify the original source.

Do attitudes differ between Japan and other countries?

“The USSR (Russia) banned microwave ovens” is a myth

The story that “the Soviet Union banned microwave ovens by law in 1976” still circulates online. Traced back, it comes from a 1998 magazine article that gave no evidence. A former Raytheon engineer, who bought a Soviet-made microwave oven, the “Elektronika” (around 1980), wrote that “there is no evidence of a ban” (IEEE history site, 2013). An Australian news agency’s fact-check (2024) also rated it “false,” noting that more than 2 million microwave ovens were sold in Russia in the first half of 2024.

Is the microwave oven safe?

Leaked microwaves have a limit

When the German Federal Office for Radiation Protection measured them, the amount leaking was about 1% of the limit on average. At 30 cm away it falls to 5–10% of the level at the surface, and at 1 m away to 1/30–1/100. The office states that “with technically sound equipment, there is no health risk, including for pregnant women and babies.” The FDA cautions, however, that you should not use a microwave oven whose door is warped or does not close properly.

No microwaves or radioactivity remain in food

Microwaves are not “ionizing radiation” like the X-rays used in medical imaging. They disappear when the power is switched off; they do not remain in food, and food does not become radioactive (US FDA, US Environmental Protection Agency, Cancer Research UK). The Tokyo Metropolitan Government also explains that “the electromagnetic waves of a microwave oven do not change food into something harmful to the body.”

The FDA says that most microwave oven injuries are burns from hot containers, overheated food and splattering liquid, not from microwaves.

The accidents that really are common come from “heat” and “fire”

From April 2020 through December 2025, the National Consumer Affairs Center of Japan (NCAC) received 521 consultations about accidents while using a microwave oven (80 to 100 a year).

Source: NCAC (published March 25, 2026). Only the main items are extracted.

Among cooking appliance accidents reported to the National Institute of Technology and Evaluation (NITE) from 2019 to 2023, microwave ovens were the most common at 149 of 494 cases, and about 40% of those whose cause was identified involved incorrect use or carelessness. In the Tokyo Fire Department’s jurisdiction, there were 84 microwave oven fires in 2024, and in 76 of them the fire started inside the oven.

In the NCAC’s reproduction tests:

• When about 100 g of sweet potato was heated continuously at 500 W, smoke appeared in about 8 minutes and it caught fire in about 11 minutes, and the pressure inside the oven pushed the door open
• When food residue was stuck on the cover over the microwave outlet, the microwaves concentrated there and it caught fire (in the 2021 test, in about 20 seconds)

If a fire starts inside the oven, do not open the door. Switch it off, unplug it, and wait for the fire to go out. Opening the door lets air in and makes the fire stronger (NCAC).

Sudden boiling (bumping): drinks suddenly erupt

If you overheat water, milk, coffee, miso soup and the like, they can erupt all at once when you take them out or put a spoon in. In an NCAC test, about 150 mL of coffee heated for 2 minutes at 1000 W erupted in about a minute and a half.

• Heat for a shorter time. Use the drink function if there is one
• Stir before heating. Use a short container with a wide mouth
• If you have overheated it, leave it in the oven for 1 to 2 minutes before taking it out

Eggs can burst even when hard-boiled

Steam has nowhere to escape inside the shell and membrane, so pressure rises and the egg bursts. In a test heating one raw egg at 500 W, the white spurted out in about 1 minute and the egg burst about 15 seconds later (NCAC). Even a peeled hard-boiled egg or a fried egg can burst after you take it out or when you put it in your mouth (Tokyo Metropolitan Government). There are also reports of facial burns and eye injuries (Wolf 2001 and others). Beat eggs before heating them.

What about pacemakers?

In the 1970s there were reports of microwave ovens affecting pacemakers. The FDA says that “today’s pacemakers are built to prevent electrical interference, and this problem has been largely solved.” If you are concerned, check with your doctor and the pacemaker’s instructions.

Is there any harm in eating microwaved food over and over?

The Swiss study claiming “blood changes if you keep eating it”

A frequently cited study online is by Hertel et al. in Switzerland (published in a journal in 1992). It claims that after eating food cooked in a microwave oven, hemoglobin in the blood decreased and cholesterol increased.

• Only 8 people were examined. It was also published in a journal without expert review (peer review), and it is not listed in PubMed, the medical literature database
• In 1998 the European Court of Human Rights ruled that Switzerland’s decision violated the Convention, but that ruling is about whether banning the researcher from speaking infringed “freedom of expression.” The judgment says speech should not be restricted even if “the opinion is a minority view and appears to lack basis,” and it did not recognize the study as correct

The report that “amino acids in milk change into a harmful form”

In 1989, Lubec et al. in Austria sent a short letter to the medical journal The Lancet reporting that the form of amino acids changed (L-form to D-form) in infant formula heated in a microwave oven. In later research, when milk was heated in the same way in a microwave oven and in a hot water bath and compared, there was no difference (Petrucelli 1994). Another study also says “the microwave oven is an appropriate way to heat milk” (Vasson 1998).

Do not heat breast milk or formula in a microwave oven

The Ministry of Health, Labour and Welfare (MHLW; its Japanese translation of the WHO and FAO guidelines) says not to use a microwave oven when warming milk. The reason is that heating is uneven and some parts become hot (hot spots), which could burn a baby’s mouth. The US CDC also says not to use a microwave oven to thaw or warm breast milk. The CDC also gives “nutrients are destroyed” as a reason.

As for components, one study found that when breast milk was heated to 72°C or above, the components that protect against bacteria (lysozyme and IgA) decreased substantially (Quan 1992). On the other hand, another study found no difference between microwave and hot water bath heating below 60°C (Ovesen 1996), so the issue is not “the microwave oven” itself but “the temperature getting too high” and “uneven heating.”

What about substances formed by charring?

If you only warm or steam food in a microwave oven, almost no substances from charring are formed. However, they can form in a microwave oven too if you heat food until it burns.

What really deserves care is the “container”

What studies point to as a problem is not the microwave oven itself but plastic containers and plastic wrap.

The effects on the body of eating microplastics are not yet known. We cover this in more detail in the Microplastics and Food Database.

Where Japan and other regions differ is bisphenol A (BPA). BPA is a raw material of polycarbonate and other plastics. In the EU, the European Food Safety Authority (EFSA) sharply lowered the tolerable intake in 2023, and in December 2024 the use of BPA in food-contact materials was banned. Japan began a system in June 2020 that manages the raw materials of food containers and utensils with a government-set list (the positive list system), but it has not banned BPA.

Heat resistance of plastic wrap

Source: FSCJ “Food wrap film” fact sheet (2014). Values published by major manufacturers.

The Food Safety Commission of Japan (FSCJ) says that wrapping oily food (meat, fish, tempura, croquettes) directly in wrap and heating it can push the temperature above 140°C, and recommends putting it in a deeper container so the wrap does not touch the food. Do not use wrap with the oven function.

Transfer food to glass or ceramic containers

If you are concerned about what comes out of plastic, the easiest approach is to transfer food to heat-resistant glass or a ceramic dish before heating. When buying a container, check the heat-resistance temperature and “microwave safe” on the label required by the Household Goods Quality Labeling Act. Do not heat plastic containers with no label, or disposable containers from deli food and bento (Hitachi, US Department of Agriculture). Even ceramics cannot be used if they have gold or silver patterns, because they spark.

Are there studies that followed people who kept eating it?

As far as we could find on PubMed, no study followed the relationship between how much people use a microwave oven and diseases such as cancer or heart disease. As a close example, a Canadian pancreatic cancer study (179 people) reported that microwave cooking was associated with lower risk (Ghadirian 1995), but it was one item among many dietary habits asked about, and cannot be called a cause.

The World Health Organization (WHO) says “microwave ovens that meet the standards are not harmful to health,” and the German Federal Office for Radiation Protection says “heating in a microwave oven is no more harmful than conventional cooking methods.”

On the other hand, note that a microwave oven tends to heat unevenly, and bacteria can survive. In Alaska, US, all 10 people who reheated takeout pork in a microwave oven got Salmonella food poisoning, while the 20 who reheated it in an oven or frying pan did not (Gessner 1994). In 2007, 401 people in 41 US states got Salmonella food poisoning, mainly people who ate frozen pot pies heated in a microwave oven (CDC). We cover how to heat food in How to use it well.

Does a microwave oven destroy nutrients? Comparison with boiling, grilling and stir-frying

Comparing with the Standard Tables of Food Composition in Japan

The MEXT “Standard Tables of Food Composition in Japan (Eighth Revised Edition), 2023 Supplement” lists the components of the same food raw, boiled, microwaved, grilled, stir-fried in oil and so on. Microwave cooking is listed for 5 foods: potatoes, sweet corn, broccoli, salmon and tuna (8 items when counted separately, such as with or without skin, or lean and fatty tuna).

The table values are “per 100 g after cooking,” so they cannot be compared as they are. Boiled food absorbs water and gets heavier, while microwaved food loses moisture and gets lighter. Using the formula given in the tables (value per 100 g after cooking × weight change rate ÷ value per 100 g raw), we calculated how much remains in the amount made from 100 g of raw food.

Broccoli (percentage when raw is 100, %)

Sweet corn (same)

※ Values above 100 come from variation in analysis or from heating making components easier to extract; they do not mean the amount “increased.”

• When broccoli is boiled, vitamin C, potassium and vitamin B1 drop to around half. They dissolve into the cooking water, and the water is thrown away. With the microwave oven, more than 90% remained
• But the microwave oven is not always the best. For sweet corn, more vitamin C and folate remained when boiled. Vitamin D in salmon and vitamin B6 in tuna were also lower with the microwave oven than with grilling
• β-carotene (a fat-soluble vitamin) hardly dropped with any cooking method
• The tables give analysis values for single cooking runs and do not state the microwave oven’s power, time or whether wrap was used (only sweet corn: 600 W, 5 minutes). You will not necessarily get the same result at home

Summary of studies

Kojima et al. of the National Institute of Health and Nutrition compiled about 1,300 data points from 49 papers published up to 2014. The average vitamin C retention was 46% for boiling, 63% for deep-frying, 71% for pan-frying/stir-frying, 80% for microwave ovens and 83% for steaming. The institute concludes that “steaming” and “microwave cooking” retain it relatively well. For spinach, it was 57% for boiling (83 data points) and 88% for microwave ovens (6 data points).

Where did “microwave ovens destroy nutrients” come from?

The study often cited is by Vallejo et al. of a Spanish research institute (2003). It was reported that flavonoids (a type of polyphenol) dropped by 97% in microwaved broccoli. According to reports, however, in this experiment only the microwave group had the broccoli heated while soaked in water. López-Berenguer et al. of the same institute later varied the microwave time, power and water amount and concluded that the main causes of loss are “long heating time” and “a large amount of water” (2007).

In other words, what determines the loss is not “whether it is a microwave oven” but the amount of water, heating time and temperature. Even boiling retains more with a small amount of water and a short time, and even in a microwave oven, nutrients wash out if you add plenty of water and heat for a long time. In the National Institute of Health and Nutrition’s summary as well, when chickpeas were microwaved for 15 minutes with 10 times their weight in water, only 14% of the niacin remained.

What about oxalic acid in spinach?

When spinach is boiled, oxalic acid, a component of its harsh taste (aku), goes out into the water. The Tokyo Metropolitan Government explains that oxalic acid remains with microwave cooking. On the other hand, NARO introduces a study showing that cutting spinach into 1 cm pieces and microwaving it (for example, 600 W for 2 minutes) reduced oxalic acid about as much as boiling did, without reducing lutein. For vegetables with a strong aku, soak them in water after heating (Agency for Natural Resources and Energy).

Is it true that “nutrients don’t drop if you use a microwave cover”?

What the sales pages say

On the sales pages for microwave lids and covers and for dedicated microwave cookers, we found claims such as “doesn’t let nutrients and flavor escape” and “nutrients and umami don’t escape.” For example, the hometown-tax donation (furusato nozei) site description for the dedicated microwave cooker “レンジメート プロ プラス” says, “because it keeps microwaves from reaching the ingredients directly… nutrients and flavor don’t escape.” As far as we checked, none of the pages showed data from a comparison test.

Also, when you search Rakuten Ichiba for “レンジプロテクター” (microwave protector), what comes up is mainly stain-guard mats and covers that go on top of or inside the microwave oven. In this article, we check “lids, covers and dedicated cookers” used for cooking.

Is there research to back it up?

• We found no study that compared nutrients while changing only whether a lid or cover was used (searched PubMed and J-STAGE)
• The closest is a study on steam bags for microwave ovens. When broccoli was heated in a bag, more glucosinolates remained than with ordinary microwave heating. However, other polyphenols (hydroxycinnamic acid types) decreased both in the bag and with ordinary heating (Paulsen 2021)
• Components decrease even in microwave cooking without water. In the food composition tables, only 91% of vitamin C in broccoli, 46% in unpeeled potatoes and 66% in sweet corn remained after microwave cooking. This is because vitamin C also breaks down with heat and air (oxygen)

Conclusion: it may “make losses smaller,” but we cannot say they “disappear”

What greatly affects how much remains is not the cover but the amount of water and the heating time. Even if a product description flatly states that it “keeps nutrients in,” if it does not say compared with what, which components, and how much remains, there is no way to verify it.

The Act against Unjustifiable Premiums and Misleading Representations prohibits labeling that makes a product’s quality look significantly better than it is, and the Consumer Affairs Agency can require the submission of materials supporting a claim (the rule on advertisements lacking substantiation). Among cooking appliances, cease-and-desist orders were issued to 7 companies over “carb-cut rice cookers” in 2023–2024 (one company’s order was finally revoked by a court ruling in June 2026).

How to use it well

Converting wattage

Calculate the time as “labeled wattage × labeled time ÷ wattage you are using” (Panasonic). If something labeled for 600 W is heated at 500 W, about 20% longer is a guide (Yamagata Prefecture).

These are calculated guides. There are three points to note:

• The Japan Frozen Food Association recommends heating frozen food at 500 W or 600 W. High power such as 1000 W, or the automatic “warm” button, can cause overheating and uneven heating
• Some household “1000 W” models offer it only for up to 3 minutes and only for set menus (Hitachi’s instruction manual). You may not be able to set times exactly as converted
• What you use for conversion is the “high-frequency output.” It is different from the “power consumption” printed on the unit (for example, 1,450 W)

Using wrap

Panasonic’s instruction manual explains: “snug at the rim of the container, loose (fluffy) over the food.” Stretching it tight could cause bursting. Hitachi publishes a list of which foods to wrap and which not to.

Source: Hitachi, “Do I need wrap when reheating?”

Use 75°C as a guide when reheating

Microwave ovens tend to heat unevenly, and bacteria can remain in cold spots.

• The MHLW gives “75°C or above” as the guide for reheating, and the US Department of Agriculture gives “165°F (74°C)”
• Stir or rotate partway through. After heating ends, let it stand a moment before checking the temperature (US Department of Agriculture)
• For a large piece of meat, heat it longer at lower power rather than briefly at high power (same source)
• Do not heat partway and finish heating the rest later (same source)

How to heat frozen rice

• Wrap freshly cooked rice in portions of one bowl (about 150 g), flattened to 2–3 cm thick (Hitachi). If it is rolled into a ball or thick, it is harder to heat through
• Use “warm” rather than “defrost.” About 2 minutes 40 seconds to 3 minutes at 600 W is a guide (an example for a Hitachi model)
• Storage is about 1 month (Panasonic)
• One study found that a 150 g portion tasted close to rice before freezing, while a 300 g portion lost flavor because of uneven heating (Shibata et al. 2010; the co-authors include a manufacturer’s employee)

If you keep rice warm in a rice cooker for 4 hours or more, freezing it and reheating it in a microwave oven uses less energy (Agency for Natural Resources and Energy).

Microwaving is the cheaper way to prep vegetables

According to the Agency for Natural Resources and Energy, prepping 100 g of vegetables in a microwave oven instead of boiling them on a gas stove, once a day, saves about ¥860 to ¥1,000 a year.

Hitachi’s tips include wrapping the vegetables snugly in plastic wrap without draining off the wash water, arranging broccoli florets with no gaps, placing whole potatoes around the edge with the center left open, flipping root vegetables over after heating and letting them stand 3 to 5 minutes, and putting spinach in water right after heating. For vegetables in simmered dishes too, microwaving them first and then adding them to the pot reduces gas cost and cuts down on breaking apart (Agency for Natural Resources and Energy).

Thawing meat and fish

Hitachi gives the following guidance:

• Thaw right after taking it out of the freezer (if it starts melting from the outside, heating becomes uneven)
• Remove the wrap or packaging and place it in the center
• Cover thin or narrow parts with aluminum foil (be careful: if the foil touches the walls or door inside the oven, it will spark)

The US Department of Agriculture recommends cooking meat and fish thawed in a microwave oven right away, because some parts have started to warm.

Heat frozen food at the wattage on the label

For frozen food, the basic rule is to heat it manually at the wattage and time printed on the package (Japan Frozen Food Association). Using the automatic “warm” button, high power, or heating different frozen foods together can lead to under-heating or overheating. Thawing a product that is meant to be heated frozen before heating it is also a cause of overheating.

For people who want to choose frozen side dishes by their ingredients, there is a home-delivery frozen side dish service that says its food is cooked without additives. We compare grocery delivery services in our grocery delivery comparison article.

A cooker for making grilled fish in the microwave oven

Instead of a fish-grilling grill, there are dedicated cookers that can grill fish in a microwave oven. The manufacturer explains that the best-known one, “レンジメート プロ,” uses a ceramic-coated lid to keep microwaves from reaching the food directly, and gives food a browned surface as if pan-fried. The inside of the body has a “fluoropolymer coating” (ふっ素樹脂塗膜加工; so-called Teflon coating; see our Teflon-coated cookware article for details).

Because this is a different kind of heating from warming with microwaves alone, follow the times and usage in the instruction manual. The manufacturer writes that it should not be used with the oven or grill functions or automatic menus. Among the accident consultations received by the NCAC, there were also 30 involving “microwave grill cookers.”

Is it OK to use it to sanitize a sponge?

In an experiment at a US Department of Agriculture laboratory, heating a wet sponge in a microwave oven for 1 minute killed 99.99999% of bacteria (2007; paper by Sharma et al. 2009). However, the paper notes that a dry sponge or a sponge with a metal scrubber is a fire hazard. Also, in a 2017 German study, even the sponges of people who said they “sanitize regularly” did not have fewer bacteria, and the study recommends replacing sponges regularly, such as once a week (Cardinale 2017).

The instruction manuals of Japanese manufacturers say “do not heat anything other than food” (Hitachi). Because this is a use the manufacturers do not approve, we do not recommend it in this article.

What not to do

In a Tokyo Metropolitan Government survey of 1,012 people (2015), about 80% had used it in a way that required caution, and more than 60% had used it with a dirty interior. About 30% used it without looking at the instruction manual or the warnings on the unit.

Care, power costs, lifespan and disposal

Cleaning the interior

According to the Tokyo Metropolitan Government, about 40% of microwave oven accidents are caused by dirt such as food residue turning to carbon. The basic approach is to wipe often with a tightly wrung damp cloth.

For cleaning with baking soda or citric acid, manufacturers say different things. Iris Ohyama introduces a method of heating baking soda water or citric acid water to loosen dirt with the steam. Hitachi advises against using them, saying that wiping hard with citric acid or baking soda can peel the paint and leave white stains. Checking the instruction manual for your own model is the surest way.

Power costs

Calculated at ¥31 per kWh (a guide from the Electric Home Appliances Fair Trade Council). The national energy-saving standard calculates annual power consumption assuming the microwave oven is used 1,164 times a year (about 3.2 times a day). Heating at high power shortens the time, so the electricity cost does not change much (Panasonic).

Watch out for 50 Hz and 60 Hz

The electricity frequency differs between eastern Japan (50 Hz) and western Japan (60 Hz) (the boundary is roughly Itoigawa in Niigata Prefecture and the Fuji River in Shizuoka Prefecture). Most combination ovens are “hertz-free” and work on both, but some microwave-only models are still 50 Hz-only or 60 Hz-only (Hitachi, Haier). If the nameplate on the unit says “50-60Hz,” it works on either. If you move between east and west, some models need parts replaced.

Lifespan and disposal

• Microwave ovens are not among the 5 products (electric fans, ventilation fans, air conditioners, washing machines, CRT TVs) that are required to display a “designed standard period of use.” In creating the national energy-saving standard, the years of use were assumed to be about 10. Manufacturers keep repair parts for 8 years after production ends (Hitachi, Panasonic)
• If the door is cracked or warped, the turntable doesn’t turn, or it makes strange noises, stop using it and ask for an inspection
• It is not one of the 4 items under the Home Appliance Recycling Law (air conditioners, TVs, refrigerators, washing machines). It is covered by the Small Home Appliance Recycling Act, but how it is collected differs by municipality. For example, in Sakai City it does not go in the small-appliance collection boxes and is bulky waste (fee of ¥800)

Recommended microwave ovens and how to choose

What to decide first

Because the basic rule is to heat frozen food at 500 W or 600 W (Japan Frozen Food Association), it also helps to check that you can choose 600 W and 500 W manually. On price, in Kakaku.com’s best sellers (2024), about 80% were ¥60,000 or less. Sales-volume share by manufacturer was not published in the range that can be viewed for free.

Example models (official specifications and Rakuten Ichiba prices checked on October 2, 2026)

Source: each manufacturer’s specifications page. Prices may change.

Microwave-only models

If you mainly warm, defrost and prep vegetables, a microwave-only model is enough. All three have a flat interior and work on both 50 Hz and 60 Hz.

Microwave ovens with oven (23 L class)

For people who also want to bake bread and sweets or make grilled dishes. The capacity suits about two people.

Steam (superheated steam) combination ovens (30 L)

Higher-end models for people who also want to steam food and cook in the oven using steam.

Summary

Items featured in this article

Item featured	When it helps	Where to buy
イワキ パック＆レンジ (heat-resistant glass)	When you are concerned about heating plastic containers	See on Rakuten (sobani) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
HARIO heat-resistant glass storage containers	Same as above	See on Rakuten (HARIO公式NETSHOP) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR 【HARIO NETSHOP】 PR
Skater official shop	Microwave-safe resin containers and lunch boxes	【スケーター公式ショップ】 PR
タニタ デジタル温度計 TT-583 (Tanita digital thermometer)	When you want to check that reheated food reached 75°C	See on Rakuten (楽天24 ヘルスケア館) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
Frozen rice containers	When you want to freeze rice one bowl at a time	See on Rakuten (お弁当グッズのカラフルボックス) PR
FIT FOOD HOME	When you want to choose side dishes to microwave by their ingredients	【国産素材】無添加調理“FIT FOOD HOME”。 PR
レンジメート プロ	When you want to make grilled fish in the microwave oven	See on Rakuten (MUK ショップ（公式）) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
Panasonic NE-FL1E (microwave-only, 22 L)	When you mainly warm, defrost and prep	See on Rakuten (Panasonic Store Plus（公式）) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
Sharp RE-TD186 (microwave-only, 18 L)	Same as above (1 to 2 people)	See on Rakuten (イーベストPC・家電館) PR See on Yahoo! Shopping PR
Iris Ohyama IMB-FD2204 (microwave-only, 22 L)	Same as above	See on Rakuten (アイリスオーヤマ公式) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
Panasonic NE-FS3E (combination oven, 23 L)	When you also want to bake bread and make grilled dishes	See on Rakuten (Panasonic Store Plus（公式）) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR
Toshiba ER-60C (square-tray steam combination oven, 23 L)	Same as above	See on Rakuten (ケーズデンキ) PR See on Yahoo! Shopping PR
Sharp Healsio AX-N1D (30 L)	When you also want to steam food and use superheated steam	See on Rakuten (楽天ビック) PR See on Yahoo! Shopping PR
Panasonic Bistro NE-UBS10E (30 L)	Same as above	See on Rakuten (Panasonic Store Plus（公式）) PR See on Amazon.co.jp PR See on Yahoo! Shopping PR

Sources

History and how it works

• US Patent US 2,495,429, “Method of Treating Foodstuffs” (P. L. Spencer, filed October 8, 1945; granted January 24, 1950) https://patents.google.com/patent/US2495429A/en
• IEEE Spectrum, “A Brief History of the Microwave Oven” (2016); American Physical Society, APS News (October 2015); Smithsonian Magazine (2017)
• Toshiba Lifestyle, “PRODUCT HISTORY: Microwave Ovens and Combination Ovens” and “The Story of Japan’s First Unit”; Sharp, “Product Story”; Kaden Watch, “Sharp: Tracing the History of ‘Sincerity and Creativity,’ Part 5” (2010)
• M. Chaplin, “Water and Microwaves” (London South Bank University) https://water.lsbu.ac.uk/water/microwave_water.html
• Tanaka M, Sato M. Microwave heating of water, ice, and saline solution. J Chem Phys 2007;126:034509 (PMID 17249886)
• Radio Act Enforcement Regulations, Article 46-7 (e-Gov Law Search); Ministry of Economy, Trade and Industry (METI), “Interpretation of the Ministerial Ordinance Establishing Technical Standards for Electrical Appliances and Materials,” Appended Table 8
• National Institute of Technology and Evaluation (NITE), Accidents involving cooking appliances (September 26, 2024 and September 25, 2025)

Ownership around the world and attitudes

• Cabinet Office, “Consumer Confidence Survey,” ownership rates of major durable consumer goods (1970–2004); Ministry of Internal Affairs and Communications (MIC), “National Survey of Family Income, Consumption and Wealth” (2009 and 2014)
• US Energy Information Administration, “Residential Energy Consumption Survey 2020,” Table HC3.1
• Statistics Canada (2009); UK Office for National Statistics, Family Spending Table A45; Central Statistics Office, Ireland, SILC (2019); France INSEE, “Tableaux de l’économie française 2019”; Federal Statistical Office of Germany, “Ausstattung mit elektrischen Haushaltsgeräten”; Censis, “1° Rapporto Auditel-Censis” (2018); National Bureau of Statistics of China, China Statistical Yearbook 2012
• Shahab L, et al. Prevalence of beliefs about actual and mythical causes of cancer. Eur J Cancer 2018;103:308-316 (PMID 29705530)
• J. Osepchuk, “There Was No Ban on Microwave Ovens in the USSR,” ETHW (2013); AAP FactCheck (December 23, 2024)

Safety and health

• US FDA, “Microwave Ovens”; US federal regulation 21 CFR 1030.10; US Environmental Protection Agency, RadTown; German Federal Office for Radiation Protection, “Microwave ovens”; WHO, “Radiation: Electromagnetic fields” Q&A
• Tokyo Metropolitan Government Bureau of Public Health, Food Safety FAQ; Tokyo Metropolitan Government Bureau of Citizens and Cultural Affairs, materials on preventing hazards from “microwave ovens” (2015 and 2026)
• NCAC, “Prevent Accidents Caused by Microwave Ovens!” (March 25, 2026); NCAC, “From Tests for Resolving Consultations,” Nos. 150 and 151 (2021)
• European Court of Human Rights, Hertel v. Switzerland judgment (August 25, 1998, application no. 25181/94)
• Lubec G, et al. Lancet 1989 (PMID 2574327) / Petrucelli L, Fisher GH. J Am Coll Nutr 1994 (PMID 7911811) / Vasson MP, et al. Amino Acids 1998 (PMID 9891762)
• Quan R, et al. Pediatrics 1992 (PMID 1557249) / Ovesen L, et al. Int J Food Sci Nutr 1996 (PMID 8889628)
• MHLW, “Guidelines for the Safe Preparation, Storage and Handling of Powdered Infant Formula” (provisional translation); US CDC, “Breast Milk Storage and Preparation”
• Felton JS, et al. Food Chem Toxicol 1994 (PMID 7959444) / Sugimura T, et al. Cancer Sci 2004 (PMID 15072585) / Takatsuki et al. J Food Hyg Soc Jpn 2004 (PMID 15168561) / Yuan Y, et al. J Food Sci 2007 (PMID 17995763)
• Hussain KA, et al. Environ Sci Technol 2023 (PMID 37343248) / Gerhard MN, et al. Food Addit Contam A 2022 (PMID 34732109) / He YJ, et al. J Hazard Mater 2021 (PMID 34015709) / Moreira MA, et al. 2014 (PMID 24380980)
• FSCJ, “Food wrap film” fact sheet (2014); Consumer Affairs Agency, “Positive list system for food utensils, containers and packaging”; EFSA, “Bisphenol A”
• Ghadirian P, et al. Cancer Epidemiol Biomarkers Prev 1995 (PMID 8634663) / Gessner BD, Beller M. Am J Epidemiol 1994 (PMID 8166140) / CDC MMWR 2008 (PMID 19037195)

Nutrition and covers

• MEXT, “Standard Tables of Food Composition in Japan (Eighth Revised Edition), 2023 Supplement,” main table and Table 12, “Summary of cooking methods and weight change rates” https://www.mext.go.jp/a_menu/syokuhinseibun/mext_00001.html
• Kojima A, et al. “Literature survey on losses of water-soluble vitamins by cooking.” Vitamins 2018;91(2):87-112
• Ohba K. Journal of Home Economics of Japan 1988;39(10):1051 / Song L, Thornalley PJ. Food Chem Toxicol 2007 (PMID 17011103) / Pellegrini N, et al. J Agric Food Chem 2010 (PMID 20218674) / Lee S, et al. Food Sci Biotechnol 2018 (PMID 30263756)
• Vallejo F, et al. J Sci Food Agric 2003;83:1511-1516 / López-Berenguer C, et al. J Agric Food Chem 2007 (PMID 17979232) / Paulsen E, et al. Food Res Int 2021 (PMID 33648297)
• NARO, “A heating method to reduce oxalic acid in spinach” (research exhibits 2019 and 2022)
• Consumer Affairs Agency, “What is misleading representation of quality?” and the cease-and-desist orders on “carb-cut rice cookers” (2023 and 2024)

Use, power costs and lifespan

• Panasonic, “What is the ‘wattage’ of a microwave oven?”; Hitachi, “Microwave Oven FAQ” (wrap, blanching, thawing, frozen rice, frequency, care); Hitachi MRO-VS8 instruction manual
• Yamagata Prefecture Okitama Public Health Center, “Easy Microwave Menu Collection”; Japan Frozen Food Association, “How to Cook Frozen Food Well” and “Frozen Food Production and Consumption in Reiwa 7 (Preliminary Report)”
• MHLW, “Six Points for Preventing Food Poisoning at Home”; US Department of Agriculture FSIS, “Cooking Safely in the Microwave Oven”
• Shibata et al. Journal of Cookery Science of Japan 2010;43(2):87
• Agency for Natural Resources and Energy, “Energy Saving Portal,” Kitchen; Energy-saving product information site, “How to Use and Choose Energy-Saving Appliances: Microwave Ovens” (2025); Advisory Committee for Natural Resources and Energy, Microwave Oven Judgment Criteria Subcommittee, final summary
• US Department of Agriculture Agricultural Research Service, “Best Ways to Clean Kitchen Sponges” (2007); Sharma M, et al. Food Control 2009; Cardinale M, et al. Sci Rep 2017;7:5791 (PMID 28725026)
• METI, “Long-Term Product Safety Labeling System”; Sakai City, “Small Appliance Collection Box Quick Reference” and “Bulky Waste Disposal Fee Schedule”

Choosing one

• Specifications pages from Panasonic (NE-FL1E, NE-FS3E, NE-UBS10E), Sharp (RE-TD186, AX-N1D), Toshiba Lifestyle (ER-60C) and Iris Ohyama (IMB-FD2204) (checked October 2, 2026)
• Iris Ohyama, “How to Choose a Microwave Oven”; Hitachi, “Differences Between Sensors”; Sharp, “About Frequency (50 Hz and 60 Hz)” and “Containers You Can and Cannot Use”; Panasonic, “Is It OK to Heat Plastic in a Microwave Oven?”
• Kakaku.com Magazine, “How to Choose a Microwave Oven or Combination Oven” (September 2024)
• Consumer Affairs Agency, “Synthetic Resin Products Quality Labeling Regulations”