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There is much fear-mongering about radiation these days; the damaged Japanese reactor affecting the US, the safety of nuclear power, x-rays, body scanners, etc. But before we go and worry ourselves to death about the alpha and beta wrecking balls of nature melting our faces off, we should also know just how dangerous radiation really is.

The situation in Japan is dangerous, but it will have no effect on Americans. Meanwhile, Americans are scared of the radiation used to scan their private parts in airports, and begs the question: are airport body scanners safe?

I recently had the pleasure of getting my testes examined in one of Denver International Airport’s fine full body scanning stations. As I calmly wondered what my naked body looked like via x-ray, I remembered that the public is pretty scared of these things. Let’s put the potential invasion of privacy rights aside for a moment, as this is a science blog, and talk about the “dangers” associated with the airport full-body scan.

Dangers of Radiation

What people are scared about is the potentially harmful ionizing radiation that x-rays are composed of. Ionizing radiation is dangerous because this type of radiation can strip electrons from atoms and molecules, thus altering body chemistry, and potentially causing cancer. This of course sounds scary, and is largely the reason why people have apprehensions about the airport scanners. However, with any kind of radiation, the key component to harm or lethality is dosage.

Radiation All Around You

We are exposed to radiation from natural sources all the time. The average person in the U.S. receives an effective dose of about 3 mSv (milli-sieverts) per year from naturally occurring radioactive materials and cosmic radiation from outer space. These natural “background” doses vary throughout the country.

People living in the plateaus of Colorado or New Mexico receive about 1.5 mSv more per year than those living near sea level. The added dose from cosmic rays during a coast-to-coast round trip flight in a commercial airplane is about 0.02 mSv. Altitude plays a big role, but the largest source of background radiation comes from radon gas in our homes (about 2 mSv per year). Like other sources of background radiation, exposure to radon varies widely from one part of the country to another. And, as we will see below, these doses just from being alive on this planet for one year are 2000-3000 times greater than any body scan.

Understanding Radiation Exposure

What if you hid the gun…rectally?

Government officials have set the recommended limit of radiation exposure from security scanners at 250 microsieverts, which would require 12,500 airport screenings a year to exceed. Below, a chart of some common exposures to radiation, measured in microsieverts, a unit that measures the biological effects of radiation.

Screening at an airport X-ray scanner .02 microsieverts
Negligible risk 10 microsieverts/year
Transcontinental flight 20 microsieverts
Average yearly radiation exposure from the environment 3000 microsieverts
Chest X-ray radiation exposure 100 microsieverts
Mammogram 700 microsieverts
Abdominal CT scan 10,000 microsieverts
Enough to cause radiation sickness 1,000,000 microsieverts
Enough to cause death 6,000,000 to 8,000,000 microsieverts

That should make it pretty obvious, but let’s spell it out anyway. You receive 2,000 times more radiation due to cosmic x-rays from space just flying than you did getting scanned to board the flight! You would have to get 5,000 body scans to equal just one chest x-ray, and you all have had many of those. For my money, 500 times less than negligible is absolutely harmless. Think about it, you get the equivalent of 150,000 body scans a year just by living on this planet!

The amount of radiation from one full-body airport scan is equivalent to two minutes of flying in an airplane, to sleeping next to another person for the night, and to 40 minutes of just living. All those are of course harmless, and our bodies are perfectly adapted to deal with such doses. Evolution has weeded out those organisms whose body chemistry could not deal with background cosmic and low-level radiation, otherwise life (including us) wouldn’t even be here (unless it could adapt to the constant radiation).

Of course, being that we are adapted to these low-level radiation doses, this means that we are not able to handle high-level doses. This is why the situation in Japan, like Chernobyl, can be deadly.

What Does Radiation Do To You?

For the morbidly curious: One firefighter who was assigned to fight the fire immediately after the Chernobyl meltdown entered the site with no protection; he was wearing jeans and a t-shirt. This exposed him to just about the highest dose of radiation that one could get. He was admitted to the hospital by nightfall. Within a week, his skin was peeling off in layers, and he began to cough up pieces of his lungs as his body basically disintegrated from the inside. His dose had been so severe that nurses were not able to come near him; he was separated by a sealed partition which would keep the high amounts of radiation that his body was now a conduit for, at bay. –from the book Voices From Chernobyl

Of course, the airport is dealing with radiation that is nowhere near these levels, and you have nothing to worry about if the machines are working properly, well-maintained, and are actually putting out the dosage they claim.

Not Even the Dangerous Kind

So we have laid out how the airport body scanners emit radiation that is 500 times less than negligible, but this could still be risky if we were exposing our vital organs right?

Actually, the most common model of airport body scanner uses back-scatter x-ray technology. In this technique, x-rays are not passed through your body, like in medical x-rays, but reflected off your skin, barely penetrating more that a few millimeters. In other words, the scanner bounces harmless levels of x-rays off your body and reads the reflected “image”. The scan is not penetrating, not coming in contact with any vital organs. But again, even if it did, your body receives much more radiation just by living on this planet.


The new scanners may be an invasion of privacy, and nobody wants to see you naked, but as far the science goes, the new scanners are harmless. Not convinced? Here’s a brand new medical study that at least preliminarily concludes the same.