Is it safe to heat food in a microwave oven?
Recently, claims that microwave-heated food produces carcinogens, that the nutritional value of food is lost, and that microwave radiation damages the brain have been making a comeback. Today, starting with why microwaves can heat food, we will introduce the characteristics of microwave ovens and debunk the myths about their dangers.
Why can microwave ovens heat food?
Let's start with water. A water molecule is composed of one oxygen atom and two hydrogen atoms. The oxygen atom has a strong attraction for electrons, so the electrons in the water molecule are more concentrated on the oxygen atom side. As a result, the water molecule has a positive charge on one end and a negative charge on the other. In chemistry, such a molecule is called a "polar molecule."
In normal water, water molecules are arranged randomly, with positive and negative charges pointing in all directions. When water is in an electric field, the positively charged end will turn towards the negative pole of the field, and the negatively charged end will turn towards the positive pole—the so-called "opposites attract, likes repel."
If it were a static electric field, the water molecules would line up and then become still. If the electric field keeps rotating, the water molecules will follow, trying to maintain alignment with the field. If the electric field rotates very quickly, the water molecules will also rotate quickly. Similar to friction generating heat, the temperature of the water rises.
Electromagnetic waves are just such a rotating electric field. The electromagnetic waves used in microwave ovens rotate billions of times per second. Water molecules rotating at this speed will naturally become "hot all over," and the temperature rises sharply in a short time. Once the microwaves stop, the rotating electric field disappears, and the water molecules become calm again. In this process, the water molecules themselves are not changed by the microwaves.
Not only water, but other polar molecules can also be heated by microwaves. Most foods contain water and other polar molecules, so they can be quickly heated by microwave energy. Non-polar molecules, such as air and some containers, will not be heated. When we heat food and feel the container is hot, it is usually because the hot food has "scalded" the container.
Does microwave heating cause cancer?
Because microwaves are a form of radiation, many people naturally assume they cause cancer. Microwaves are electromagnetic waves, essentially the same as the waves used in radios and telegraphs, as well as infrared rays and visible light. The difference between them lies only in their frequency. The frequency of microwaves is higher than that of radio waves but lower than that of infrared rays and visible light. Since radio waves and visible light do not cause cancer, it is not difficult to understand that microwaves, with a frequency between them, also do not cause cancer. In fact, the "radiation" here only refers to the fact that the energy of microwaves can be emitted; it is different from the radiation produced by X-rays and radioactive isotopes. Although X-rays are also electromagnetic waves, their frequency is much higher than that of microwaves, and thus their energy is higher. Radioactive isotopes emit particles during their decay process, which can cause cancer in living organisms.
Microwaves do not cause cancer in humans, nor do they cause food to produce carcinogens. In fact, they can even help prevent the formation of carcinogens. For foods like fish and meat, traditional heating methods, especially grilling, roasting, and frying, can easily cause the meat to char, producing some carcinogens. Using a microwave oven to heat them can effectively reduce the production of such carcinogens.
Is it safe to use a microwave oven?
Sunlight is a higher-energy electromagnetic wave than microwaves. Is sunlight safe?
The safety of microwaves is the same as that of sunlight—whether it harms the human body depends on the strength of the energy. Gentle sunlight is pleasant, but scorching sun can cause serious sunburns. Microwaves are the same way—since they can heat food, they can naturally heat the human body. The key question is: how much energy is left in the microwaves when they reach the human body?
Scientists have conducted extensive research for us and have found the minimum microwave power that can cause harm to the human body. In a well-functioning microwave oven, the power of leaked microwaves is far from the level that can harm the human body—the U.S. regulation is that at a distance of about 5 cm from the oven, the power does not exceed 5 milliwatts per square centimeter; China's standard is even stricter, at 1 milliwatt. Moreover, the energy of microwaves decreases with the square of the distance. That is, if the power is 1 milliwatt at 5 cm, it drops to one-hundredth of a milliwatt at 50 cm, making it "harmless to humans and animals."
In general, the claims that microwave ovens "cause cancer" or "produce harmful substances" are all rumors. Although microwave ovens can hardly help us make very delicious food, the convenience and speed they bring are their great advantages. For the elderly and children, using a microwave oven to heat meals is also much safer than using an electric or gas stove.
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Microwave oven injuries are often due to improper use
Many "accidents" involving injuries from using a microwave oven have nothing to do with the oven itself but are caused by improper use. As long as you avoid using the microwave oven incorrectly, accidents will not happen. Here are the two most common types of accidents:
1. Superheated liquids. When water is traditionally boiled, it circulates, and when it reaches the boiling point, it "boils." With microwave heating, the water does not circulate; its temperature just rises, possibly exceeding the boiling point without "boiling." However, the water at this point is already at a very high temperature, and with any disturbance, it will boil violently. If this disturbance occurs when you reach for the container, you will be scalded more severely than by boiling water. The cleaner the container and the cleaner the water, the more likely such an accident is to happen. Therefore, for safety's sake, it's best not to "test it on yourself." Other liquids, like milk or soup, are less likely to overheat because they contain other ingredients, but they can also "erupt" and overflow the container if heated for a long time. It's not that you can't use a microwave to heat these things, but you must calculate the heating time correctly.
2. Exploding eggs. You cannot heat eggs in a microwave oven. The reason for an egg exploding is somewhat similar to the "violent boiling" of water. The inside of the egg becomes overheated and builds up great pressure. When disturbed from the outside, the pressure is released, and the egg explodes. If the explosion happens when the egg is in your mouth, it would be like setting off a firecracker in your mouth.