Do Cell Phones Cause Cancer?
Claims of cell phones causing brain cancer are becoming common. An examination of the basic properties of electromagnetic radiation and suntanning shows that this cannot be true.
The Back Story
Three billion people use cell phones on a regular basis. That makes eight billion pounds of brain matter being subjected to cell phone radiation every day. Is this cause for concern? For a lot of people the answer is yes. The media has seized on this concern to raise the alarm. In March of 2008 the British newspaper the Independent reported that a study by Dr. Vini Khurana shows that mobile phones could kill more people than smoking. The story was quickly repeated on this side of the Pond by Fox News. A few months later Tara Parker-Pope of the New York Times stirred the pot with two stories, Experts Revive Debate Over Cellphones and Cancer and How Much Radiation Does Your Phone Emit?. In an alarming introduction, the first article says,"Along with Senator Edward M. Kennedy's recent diagnosis of a glioma, a type of tumor that critics have long associated with cellphone use, the doctors' remarks have helped reignite a long-simmering debate about cellphones and cancer."Cnet has done us the wonderful service of rating cell phone power levels, or, more ominously, "measuring the quantity of radiofrequency energy that is absorbed by the body". Finally, the Food and Drug Administration says there is no evidence of health problems associated with cellphone use, but the FDA adds that there also is no proof "that wireless phones are absolutely safe."
So there you have it, the FDA says there is no proof that cell phones are safe, some doctors and their studies say that cell phones are unsafe, Ted Kennedy has brain cancer, and billions of people are going to die horrible deaths.
But before you dunk your cell phone in the toilet (again) and wrap your head in tin foil, how well do these claims stand up to science and common sense?
Light Basics
First we need to clarify that the "radiation" we are talking about is electromagnetic radiation. Electromagnetic radiation can be thought of as a wave with two properties, wavelength and wave amplitude. Wavelength is a measure of the distance between peaks of a wave, while the amplitude measures the height of a wave. If you are a boater you can appreciate that short wavelengths make for choppy waters while large wave amplitudes can be pretty darn scary. "Radio waves", "microwaves", "UVA", and "light" are all types of electromagnetic radiation that differ only in their wavelength. All of this together is called the spectrum of light.
You are probably more familiar with characterizing radiation by frequency. The frequency of a wave is how many times it oscillates per second (the unit of this is called a Hertz, abbreviated Hz). Frequency is related to wavelength by the formula c = wavelength x frequency, where c is the speed of light, about 300 thousand kilometers per second. (In case you are wondering, this is the same c that appears in Einstein's formula E = m c2.) We can use the equation to freely translate between frequency and wavelength -- they are just different ways of characterizing one of the properties of radiation.
It is also possible to think of electromagnetic radiation in terms of particles, called photons. This is the famous "wave-particle duality" quantum mechanical nature of light (sorry, but that's the way it is). Photons always move at the speed of light but can have different energy. The connection between the wave and the particle picture is provided by Planck's Law, which states that the photon energy is inversely proportional to the radiation wavelength. In other words, the shorter the wavelength the higher the energy. You can refer to the figure above or the table to see the translation between wavelength, frequency, and energy.
| name | frequency | wavelength | energy (eV) | energy (j) |
|---|---|---|---|---|
| x-ray | 1 billion GHz | 0.3 nm | 4,000 | 6 10-16 |
| UVB | 1 million GHz | 300 nm | 4 | 6 10-19 |
| UVA | 750,000 GHz | 400 nm | 3 | 5 10-19 |
| visible | 430,000 - 750,000 GHz | 400 - 720 nm | 1.7 - 3 | (2.7 - 5) 10-19 |
| microwaves | 10 Ghz | 3 cm | 4 10-5 | 6 10-24 |
| cellphone radio | 1 Ghz | 30 cm | 4 10 -6 | 6 10-25 |
| FM radio | 100 Mhz | 3 m | 4 10-7 | 6 10-26 |
Check it! You can measure the wavelength of microwaves by covering a plate with marshmallows and microwaving them. Use low power and turn off the turntable. You should see spots of melted marshmallow about 7 cm apart (this depends on the frequency your microwave works at)! I tried this and got a gooey mess, let me know if you can get it to work!
A word about the units in the tables. A meter (m) is about 3 feet, a centimeter (cm) is about the height of your little finger. A nanometer
(nm) is 10
One other thing about light: it interacts with matter by bouncing off of charged particles, mostly
electrons in the outer orbits of atoms and molecules. Light is absorbed by a brick because the brick
is dense with electrons that love to interact with visible light. Glass is transparent because
the electrons that help make it up do not play well with visible light.
To be fair to Parker-Pope, she does say,
Sounds pretty definitive to me! But there is a possible catch:
Does their claim stand up to scrutiny? Wi-Fi radiation has a frequency of around 2.4 GHz, similar to cell phone radiation, making it about
500,000 times too weak to cause DNA damage. Thanks anyway, BBC.
Light and Cancer
Can electromagnetic radiation cause cancer? Yes! This is the reason your dental assistant leaves the room
when she x-rays your loose tooth. Lead does a good job of absorbing x-rays, which is why that apron that
covers your delicate bits is heavy. Next on the list is UVB, which is also dangerous because it
causes sunburn and skin cancer.
UVA is dangerous, but in an indirect way (it creates free radicals that damage DNA). What about visible light? You've probably
seen truck drivers with tan left arms -- tan because he drives with his arm out the window and hence
exposes it to UVA and UVB radiation.
The rest of him is not tan because glass absorbs UVA and UVB radiation very well. Of course it does
not absorb visible light (otherwise we couldn't see through it!). We conclude that visible light
does not cause sunburn or skin cancer.
This is a
good thing because most of us spend 16 hours a day bathed in (mostly artificial) visible light.
Cells Gone Wild!
Why are x-rays, UVA, and UVB carcinogenic and why is visible light not? To understand this we need to
recall some things about cancer. Cancer happens when cells start reproducing in an uncontrolled
fashion. Since cell reproduction is controlled by DNA we might conclude that x-rays and other high
energy radiation damage DNA molecules in some way. In fact this is exactly what happens. Light radiation
with wavelengths less than about 300 nm have sufficient energy that they can scramble DNA base pairs when
they smash into their electrons. Visible light simply does not have enough energy to cause this kind
of damage. DNA lives in a quantum world and if a photon does not have enough energy to cause a base
pair to scramble, no amount of photons (or radiation intensity) can ever cause it to happen.
This is why you can expose your skin to visible light for hour after hour, day after day.
Cellphones Can Not Cause Cancer
What about cellphones? They typically broadcast between 800 Mhz and 2.1 GHz, which corresponds to
a wavelength of 30 cm (let's use 1 GHz for now).
The energy carried by cell phone radio waves is not sufficient to damage DNA! In fact it is about
one million times less energetic than visible light! Similarly, radio waves, TV transmissions, and microwaves
are all too feeble to cause DNA damage, and hence cancer. Cellphones do not cause cancer.
"Cellphones emit non-ionizing radiation, waves of energy that are too weak to break chemical bonds or to set off the DNA damage known to cause cancer. There is no known biological mechanism to explain how non-ionizing radiation might lead to cancer."
Of course she is implying that we don't know everything, and therefore cancer-from-cell-phones could be a real effect.
This is an example of the Incomplete Knowledge Fallacy.
What About the Doctors?
As they say, 50% of doctors graduated in the bottom half of their class. And most doctors are people
and susceptible to the same kind of self-deception and fallacies that the rest of us are. The cases
of brain cancer in cellphone users that the doctors have seen is not evidence that cellphone
use causes cancer. After all, people get brain cancer, and some of them (these days, most of them) are
going to be cellphone users. What is needed is a thorough statistical study.
What About the Studies?
Tara Parker-Pope quotes a study (Int J Cancer, 120, 769 (2007))
as providing evidence that cellphones cause cancer. Does it? As you can see yourself by following the
link, the authors say straight out:
"We found no evidence of increased risk of glioma [a kind of brain cancer] related to regular
mobile phone use".
Furthermore,
"No significant association was found across categories with duration of use, years since first use, cumulative number of calls or cumulative hours of use."
"For more than 10 years of mobile phone use reported on the side of the head where the tumor was located, an increased OR of borderline statistical significance (OR = 1.39, 95% CI 1.01, 1.92, p trend 0.04) was found, whereas similar use on the opposite side of the head resulted in an OR of 0.98 (95% CI 0.71, 1.37)"
The authors are saying that they saw a slight increase of incidence of glioma on the side of
head that the cellphone was used versus the "far" side. However, the increase is called "borderline" meaning that it could be simply due statistical fluctuations in their data. The way to make
a definitive statement is to collect a lot more data (examine a lot more patients). Of course, if the
original comparison of cancer incidence in cellphones users and non-cellphone users continues to find
no increase in the rate of cancer for cellphone users, this scenario would be impossible to explain.
Why would brain tissue 4 inches removed from a cellphone be less susceptible to cancer than that
removed by hundreds of feet? (Here I'm guessing a typical distance between a non-cellphone users brain
and somebody else's cellphone)
What About the Long Term?
Its true that the quantity of something can make a big difference; I will happily take one aspirin, but
a whole bottle is a (really) bad idea. So maybe exposure to cellphone radiation doesn't cause cancer in the short term, but what about in the long run? We know from a lot of experience that prolonged exposure
to UVA radiation increases the chance of getting skin cancer, so the long term is also not good when
it comes to UVA. Conversely people who spend a lot of times indoors (ie, exposed to visible light)
do not experience increased chances of skin cancer. Again, cell phone radiation is one million times safer than
visible radiation, so feel free to blab to your heart's content.
Science Has Been Wrong Before, it Could be Again
The argument that science has been wrong before, and therefore could be wrong again, and therefore
could be wrong here,
is an example of the Incomplete Knowledge Fallacy.
But Can You Say They are Safe?
The article from
cnet
drops the following bomb,
"Cell phones can affect internal pacemakers, but there is not conclusive or demonstrated evidence that they cause adverse health affects in humans. Conversely, there is not conclusive or demonstrated evidence that they don't cause adverse health affects in humans."
The author is saying,
you have not shown that cell phones don't cause cancer, therefore they
do (or could) cause cancer. This is called an
argumentum ad ignorantiam and is a logical fallacy similar to the negative proof fallacy. Along the same
vein,
can I prove that aliens aren't beaming persistent thoughts of Angelina Jolie into my
cerebral cortex? Can I prove that these aren't giving me cancer?
Breaking News! Wi-Fi Causes Cancer!
The BBC can whip up a frenzy just as well as Fox News and the NY Times. Performing a great public
service, they have revealed that (i) Britain is blanketed with Wi-Fi signals and (ii) that the "radiation Wi-Fi emits is similar to that from mobile phone masts.". They also "spoke to a number of scientists who questioned the safety limits and were concerned about the possible health effects of such radiation."
