Topic Overview

What is radiation?

Radiation is energy that travels as a wave or particle. Some types of radiation, called ionizing radiation, can be harmful. Radioactivity is ionizing radiation that is given off by substances, such as uranium, as they decay.

About half of the ionizing radiation we're exposed to comes from nature. It's in rock, soil, and the atmosphere. The other half comes from man-made sources like medical tests and treatments and nuclear power plants.

How much radiation is dangerous?

There is always a risk of damage to cells or tissue from being exposed to any amount of ionizing radiation. Over time, exposure to radiation may cause cancer and other health problems. But in most cases, the risk of getting cancer from being exposed to small amounts of radiation is small.

The chance of getting cancer varies from person to person. It depends on the source and amount of radiation exposure, the number of exposures over time, and your age at exposure. In general, the younger you are when you are exposed to radiation, the greater the risk of cancer.

For example:

• Someone who has had many CT scans starting at a young age is more likely to get cancer later in life than someone who hasn't had any or as many of these tests. CT scans generally use more radiation than other X-ray tests. The risk of an adult getting cancer from a CT scan is less than 1 in 1,000. The risk of a child getting cancer from the same CT scan can be much higher.^{footnote 1}
• A child who was treated with radiation for cancer is more likely to get another cancer later in life.
• A person who has been exposed to large amounts of radiation from a nuclear explosion is more likely to get cancer than someone who has not been exposed.

Exposure to small amounts of radiation doesn't cause any symptoms. But exposure to large amounts all at once may cause radiation sickness and death.

How do different sources of radiation compare?

Some sources of radiation give off larger amounts than others. For example, when you go through a full-body airport scanner, you're exposed to very small amounts of radiation. But if you live near the site of a nuclear explosion, you're exposed to large amounts of radiation.

You may be exposed to more radiation than other people if you:

• Live at high altitude.
• Have certain medical tests (such as X-rays or CT scans) or treatments (such as radiation treatment for cancer).
• Are exposed to radon gas in your home.

To understand more about radiation exposure, you may find it helpful to compare some common sources of radiation to a standard dose from a chest X-ray. A chest X-ray gives off very small amounts of radiation.

For example:

• You would need to go through a full-body airport scanner about 1,000 times to get the same amount of radiation that you would get from 1 chest X-ray.
• A 10-hour plane flight is about the same exposure as 1 chest X-ray.
• One mammogram test is about the same as 5 chest X-rays.
• Living at high altitude (such as in Calgary) for a year is about the same as having 4 chest X-rays.
• One CT scan is about the same as 200 chest X-rays.

What can you do to protect yourself?

You can't avoid radiation that occurs naturally. But there are some things you can do to reduce your exposure to man-made sources.

• If you are concerned about the risk of getting cancer from having a CT scan, talk to your doctor about the amount of radiation this test may give you. Confirm that the test is needed. Ask whether another test, such as an ultrasound or an MRI, can be done instead. In some cases, the benefits of having a CT scan outweigh the small risk of getting cancer.
• If you have concerns about radiation exposure from a full-body airport scanner, ask if you can get a pat-down instead. (But the amount of radiation exposure from one of these scanners is very low.)
• If you are exposed to radiation from a nuclear explosion:
  • Wait for instructions from public health and emergency officials to tell you what to do. Depending on the kind of explosion, authorities may advise you to shelter in place or simply to stay indoors. You don't need to leave your community unless local authorities tell you to.
  • Don't take potassium iodide (KI) tablets unless local authorities tell you to and your doctor says that it's okay. These tablets help protect your thyroid gland from the harmful effects of radioactive iodine, which can be released as a result of a nuclear explosion. They don't protect against any other radioactive substances. KI tablets can be harmful if you don't take them properly, are allergic to iodine, or have certain skin or other health problems. Some common side effects include upset stomach, skin rash, swollen salivary glands, and a metallic taste in your mouth. In rare cases, a person may have a severe allergic reaction. The reaction may cause breathing problems, hives, or swelling around the lips, tongue, or face.