Why Microwaves and Cell Phones Don't Cause Cancer
Given our daily bombardment with information, it is easy to become aware of potential threats to ourselves, but miss the resolution or the more complete explanations that follow afterward, which should put us at ease. Persistent doubts or inadvertent passing along of misinformation can lead us collectively to ignore what we know in fact (a little like the durable legend of tainted Halloween candy). Microwave ovens and cell phones (which also emit microwaves at a much lower wattage than the ovens) are thought by some to be potential causes of cancer or at least generally unhealthy additions to our modern lifestyle. This article will focus on the sources of these concerns and why (at least for now) we can leave these off of our worry list.
First, What Are Microwaves?
Microwaves are photons or waves of light (like visible or ultraviolet light) with wavelengths between 1 millimeter and 1 meter (visible light has wavelengths between 390 to 750 nanometers) as you can see in the spectrum shown below. Different wavelengths of photons or light pass through different materials to varying degrees. For example x-rays pass through most materials except metals (they appear bright in x-ray negative pictures at the doctor's office). Visible light passes easily through glass, but infrared and near infrared light (heat) does not pass through glass as easily (hence greenhouses stay warm). Microwaves can pass through many materials, but are effectively blocked by metals and water.
And That's Radiation, Right?
Microwaves are a form of radiation as scientists and engineers describe it. However, in common lay terms describing radiation, microwaves are different in that they are more closely related to heat and radio waves (just beyond the infrared) and they are less similar to ultraviolet light or x-rays (at the higher energy end of the spectrum). When most people express a concern about radiation, they are referring to ionizing radiation. This includes alpha and beta particles together with x-rays, gamma rays, and cosmic rays, and also ultra-violet light. When these forms of radiation strike molecules directly, they can sever the molecular bonds (thus creating ions).
Scientists and engineers will use the term radiation to refer to any transmission of energy across space (that is energy not conducted by touch or convected by a moving gas or liquid). So, this meaning includes "non-ionizing" radio waves, microwaves, heat from the sun, and visible light as well as "ionizing" x-rays, gamma rays, and cosmic rays.
Ionizing radiation does indeed cause harm. Ultra-violet light causes sunburns and with repeated exposure can increase the risks of skin cancer. X-rays are more powerful can even more directly damage DNA and cause cells to become cancerous with even less exposure. People who fly frequently for travel can be exposed to higher rates of cosmic rays, which are even more powerful than most x-rays. For this reason commercial pilots and astronauts have maximum exposure limits in terms to total flight hours imposed on their careers for safety reasons.
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The final type of radiation is radioactive isotopes. These are specific varieties of large atoms like certain isotopes (specific combinations of neutrons and protons in the nucleus) of uranium or iodine. These atomic isotopes can decay (split into two or more small parts) since they are unstable. This splitting can release ionizing radiation like beta or alpha particles that damage molecules. These are particularly dangerous since they cause their effects internally directly to critical organs in the body, but they need to be inhaled or ingested to seriously affect us.
So, What Happens on Exposure to Microwaves?
Microwaves exist on the energy scale in between radio waves that pass through most non-metal materials, and infrared waves that are absorbed by most materials. Microwaves are absorbed by water molecules (and to a lesser extent fats and sugars), and which then heat up increasing their temperature in proportion to the amount of energy absorbed. This interaction is called dielectric heating. This effect is much more energy efficient that the conduction and convection heat transfer associated with a stove or oven, which is why microwaves can boil water much faster than those other methods.
If your body were exposed to significant amounts of microwaves, the water in your cells near the surface (they do not penetrate far, since you are mostly made of water) would heat up in proportion to the amount of energy supplied. This effect is immediate and is easily felt by your nervous system. That is, it would burn as if you had touched something hot. Low levels of microwaves like 1 Watt cell phone transmitters do technically heat your skin too, but the amount of energy is much less than the amount of heat absorbed by your skin on a sunny day (which is at least 100 times more), or even the amount of heat passing through your skin during exercise (which can be 20 times more).
If you were exposed to the emitter in a microwave oven it would hurt, a lot. It may even cause superficial burns to your skin if you had the pain tolerance to keep yourself in range of it--most people don't. In fact, the military has been investigating just this effect as a non-lethal crowd dispersal weapon.
Exposure to microwaves from a microwave oven is very rare because the ovens include a Faraday cage, a box of metal mesh that completely absorbs the microwaves. You can see this mesh when you look through the glass door of the oven. The metallic mesh is designed such that it absorbs the microwaves of the particular wavelength that the oven emits. Microwaves do not turn corners or leak past the mesh the way that chemicals move around. From the perspective of a microwave photon, that mesh window looks like an opaque solid; it does not pass through it.
How Can We Be Confident That Doesn't Cause Cancer?
Due to what we know about the probabilistic risks of cancer in general, we can compare the rate that cancer arises in one group compared to the rate cancer arises in another group. Most exposures to carcinogens do not directly result in cancer, they only increase one's risk (the probability that they will develop cancer). This is the reason that we can say for certain that smoking causes a certain level of cancer in society overall, but cannot say for certain whether an individual's cancer was caused by their smoking (some smokers never develop lung cancer while some nonsmokers do develop lung cancer).
The conclusions of research in this area when reported in the press can be confusing, although some have tried to rectify that. The overall conclusion as the research stands today is that there is no grounds for special concern that microwave radiation from cell phones causes an increased risk of cancer.
The ideas that microwaves might cause cancer come from a few different lines of thought. First, concerns exist that microwaves from a cell phone or leaks from a microwave oven might damage DNA and other biological molecules. This makes intuitive sense because we already know that ultraviolet light can damage important cellular molecules and that x-rays are carcinogenic if received too often. But, the key here is that each photon or particle of light must have a certain amount of energy to damage molecules. Just stacking up lots of photons may cause burns due to the total amount of energy, but not result in molecular damage that would lead to cancer. As this study shows, the transition point is directly between ultraviolet wavelengths and visible blue wavelengths. Microwaves which have less energy per photon than any visible light photons, so not even approach this level. We can conclude that based on physics, microwaves are not going to be causing molecular damage to our DNA.
Second, even if the individual microwaves cannot damage DNA, might prolonged low-level exposure result in some other unanticipated effect? Shouldn't we be more precautionary? This kind of question seems scary in the sense that if there was a small effect that only appeared after years and years of exposure, we would not have sufficient data to refute it. We might never be able to run a study large enough and long enough to answer that question with hard data. But, before justifying even trying to collect information, we need to come up with a plausible mechanism that may cause the kind of damage we know leads to cancer. Low levels of warming in skin tissues has never been proposed as a potential cause of cancer. In fact, there are no existing testable hypotheses on how this entirely new cancer causing mechanism would operate. If one develops, lab tests would be in order before any additional investigation. Until such a theory has been developed, however, it would be unwise to devote large amounts of resources, when there are other much larger risks which could be addressed with those resources.
Third, there is a less well traveled belief that microwaves might make food and beverages less safe or even radioactive themselves from their absorption of microwave energy (from hence our colloquial term "nuking" comes). Something like this could be true if we were bombarding the food with alpha particle radiation, but microwaves cannot damage molecules by any mechanism other than heating them. They certainty do not have the physical capability to change the structure of atoms and make them radioactive. Microwave photons do not have sufficient energy (regardless of the oven's wattage) to ionize biological molecules and create something dangerous. If heat happens to make the food unsafe for some reason, any other cooking method would result in the same problem.
Most scientists who work in this area will never say absolutely that anything does not cause cancer. This sounds like hedging to many people, but the scientists see it as being true to the data, and they rarely ever have enough data to be mathematically certain that there is zero risk due to a given exposure. But, we can say this, if mild heating due to microwaves were to cause cancer, it must be by a wholly new and hence forth undiscovered mechanism of carcinogenesis. To demonstrate that a new cancer causing mechanism exists would require extraordinary evidence. The likelihood of such information appearing now after decades of use of these devices is rapidly vanishing.
So, What About Those Pacemaker Signs?
Microwave ovens and other powerful microwave transmitters used to pose a risk to pacemakers and some other types of electronics. This problem has essentially been eliminated today. The typical leakage path for microwave ovens is damage to the metal mesh in the window. If this is intact, there will be only insignificant leakage--although there are devices you can use to verify this yourself. Furthermore, the issue of unshielded pacemaker components susceptible to microwave exposure has been eliminated in today's devices, so even in the event of a moderate amount of microwave leakage, there is unlikely to be any problem.
Microwaves are Good
Microwave ovens are among the most energy efficient cooking appliances in any home. Using microwave ovens when appropriate is a valuable energy conservation and emissions reduction technique, especially when compared to electric stoves or ovens. While the culinary results may not be acceptable for some applications, microwave ovens are ideal for heating water and steaming methods. Cooking is one of the most universal and most inefficient uses of energy; conservation through the prudent use of microwave ovens is a valuable capability.
Microwaves transmitters like cell phone and WiFi networks enable us to have small portable data and communication devices. Radio waves cannot carry as much information as quickly as microwaves, and they require large antennas to detect and transmit them. Near infrared waves are absorbed by almost all building materials and so would require a line-of-sight transmission window with the tower to be connected (most television remotes rely on infrared technology). The modern technologies enabled by the use of these frequencies have changed the world, much of it for the better, and this includes emergency response and other applications that directly save thousands of lives. Future developments will only increase the benefits we realize from these devices.
