Health Effects of Radiation Exposure

Health Effects

This webpage provides a very brief discussion of the health effects of exposures to radiation.  More information can be found in the NRC Regulatory Guide 8.29 (Instructions Concerning Risks from Occupational Radiation Exposures) or by visiting the EHS Office and asking for other resources.

How do we know radiation causes cancer?

Basically, we have learned through observation. When people first began working with radioactive materials, scientists didn't understand radioactive decay, and reports of illness were scattered.

As the use of radioactive materials and reports of illness became more frequent, scientists began to notice patterns in the illnesses. People working with radioactive materials and x-rays developed particular types of uncommon medical conditions. For example, scientists recognized as early at 1910 that radiation caused skin cancer. Scientists began to keep track of the health effects, and soon set up careful scientific studies of groups of people who had been exposed.

Among the best known long-term studies are those of Japanese atomic bomb blast survivors, other populations exposed to nuclear testing fallout (for example, natives of the Marshall Islands), and uranium miners.

How does radiation cause health effects?

Radioactive materials that decay spontaneously produce ionizing radiation, which has sufficient energy to strip away electrons from atoms (creating two charged ions) or to break some chemical bonds. Any living tissue in the human body can be damaged by ionizing radiation in a unique manner. The body attempts to repair the damage, but sometimes the damage is of a nature that cannot be repaired or it is too severe or widespread to be repaired. Also mistakes made in the natural repair process can lead to cancerous cells. The most common forms of ionizing radiation at KUMC are beta particles and gamma and X-rays.

What kinds of health effects does exposure to radiation cause?

In general, the amount and duration of radiation exposure affects the severity or type of health effect. There are two broad categories of health effects: stochastic and non-stochastic.

Cancer and Other Stochastic Health Effects

Stochastic effects are associated with long-term, low-level (chronic) exposure to radiation. ("Stochastic" refers to the likelihood that something will happen.) Increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.

Cancer is considered by most people the primary health effect from radiation exposure. Simply put, cancer is the uncontrolled growth of cells. Ordinarily, natural processes control the rate at which cells grow and replace themselves. They also control the body's processes for repairing or replacing damaged tissue. Damage occurring at the cellular or molecular level, can disrupt the control processes, permitting the uncontrolled growth of cells cancer. This is why ionizing radiation's ability to break chemical bonds in atoms and molecules makes it such a potent carcinogen.

Other stochastic effects also occur. Radiation can cause changes in DNA, the "blueprints" that ensure cell repair and replacement produces a perfect copy of the original cell. Changes in DNA are called mutations.  Sometimes the body fails to repair these mutations or even creates mutations during repair.

Non-Stochastic Health Effects

Non-stochastic effects appear in cases of exposure to high levels of radiation, and become more severe as the exposure increases. Short-term, high-level exposure is referred to as 'acute' exposure.

Many non-cancerous health effects of radiation are non-stochastic. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function.

Medical patients receiving radiation treatments often experience acute effects, because they are receiving relatively high "bursts" of radiation during treatment.

Is any amount of radiation safe?

There is no firm basis for setting a "safe" level of exposure above background for stochastic effects. Many sources emit radiation that is well below natural background levels. This makes it extremely difficult to isolate its stochastic effects. In setting limits, regulatory agencies make the conservative (cautious) assumption that any increase in radiation exposure is accompanied by an increased risk of stochastic effects.

However, there do appear to be threshold exposures for the various non-stochastic effects. (Please note that the acute affects in the following table are cumulative. For example, a dose that produces damage to bone marrow will have produced changes in blood chemistry and be accompanied by nausea.)

  Exposure (rem)

  Health Effect

  Time to Onset
  (without treatment)

  5-10

  Changes in Blood Chemistry

 

  50

  Nausea

  hours

  55

  Fatigue

 

  75

  Hair Loss

  2-3 weeks

  90

  Diarrhea

 

  100

  Vomiting

 

  400

  Possible Death

  within 2 months

  1,000

  Destruction of Intestinal Lining

 

 

  Internal Bleeding

 

 

  and Death

  1-2 weeks

  2,000

  Damage to Central Nervous System

 

 

  Loss of Consciousness;

  minutes

 

  and Death

  hours to days

Aren't children more sensitive to radiation than adults?

Yes, because children are growing more rapidly, there are more cells dividing and a greater opportunity for radiation to disrupt the process. EPA's radiation protection standards take into account the differences in the sensitivity due to age and gender.

Fetuses are also highly sensitive to radiation. The resulting effects depend on which systems are developing at the time of exposure.

Effects of Radiation Type and Exposure Pathway

Both the type of radiation to which the person is exposed and the pathway by which they are exposed influence health effects. Different types of radiation vary in their ability to damage different kinds of tissue. Radiation and radiation emitters (radionuclides) can expose the whole body (direct exposure) or expose tissues inside the body when inhaled or ingested.

All kinds of ionizing radiation can cause cancer and other health effects. The main difference in the ability of beta particles and gamma and x-rays to cause health effects is the amount of energy they can deposit in a given space. Their energy determines how far they can penetrate into tissue. It also determines how much energy they are able to transmit directly or indirectly to tissues and the resulting damage.

Although a beta particle and a gamma ray may have the same amount of energy, inside the body the beta particle will deposit all of its energy in a small volume of tissue. The gamma radiation will spread energy over a larger volume. This occurs because beta particles have a mass that carries the energy, while gamma rays do not.

What is the cancer risk from radiation? How does it compare to the risk of cancer from other sources?

Each radionuclide represents a somewhat different health risk. However, health physicists currently estimate that overall, if each person in a group of 10,000 people exposed to 1 rem of ionizing radiation, they expect 8 more people to die of cancer than would otherwise.

Last modified: Jul 07, 2014
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