Effects of Radiation

We have a lot to be concerned about. Some people say small amounts of radiation are good for you while others say there is no amount of radiation that is safe. So why can’t someone make it easy to decide when or if you should worry about radiation exposure? That is exactly what we’re going to do here—help by providing the facts. If you want additional information on why there is disagreement about the effects of low-level radiation, we have provided this in the section titled "Controversy."

Let’s Begin

Radiation specialists use the unit “rem” (or sievert) to describe the amount of radiation dose someone received. We are going to use that unit throughout the sections. Without getting into technical specifics about that unit, it is enough to know that it indicates a measure of how much radiation energy is absorbed in our body. And, as we will see in other sections, the total energy that is absorbed and its effectiveness in causing change is the basis for determining whether health effects may result.

We’ll get into some detail later, but for a baseline—

  • 1 rem received in a short period or over a long period is safe—we don’t expect observable health effects.
  • 10 rem received in a short period or over a long period is safe—we don’t expect immediate observable health effects, although your chances of getting cancer might be very slightly increased.
  • 100 rem received in a short time can cause observable health effects from which your body will likely recover, and 100 rem received in a short time or over many years will increase your chances of getting cancer.
  • 1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death.

Safe or Not?

Why do some people say all radiation exposure is bad and others say it can be okay? Even the scientific community differs on the answer to the question of low radiation doses and health effects. Radiation can cause biological changes in cells when they are outside the human body, and these can be seen in a laboratory even when the dose is small. However, these changes are not seen or cannot be related to health effects in humans. The fact that changes can occur may make some people believe all radiation is bad and the fact that this is not related to human health effects may make others believe it is safe at low levels. The human health effects that have been observed have been when individuals or groups have received larger doses of radiation (more than 50 rem) from events like those due to military uses of nuclear weapons, accidents, and uses of radiation in medicine for therapy.

If a population receives a radiation dose of 100 rem in a short period of time, we expect health effects in some of the people who were exposed. However, many who receive a dose at that level will not have any long-lasting health effects. This is like so many other things in our lives. If we eat a high-cholesterol, high-fat diet, some of us may end up with heart disease. But that isn’t true for everyone; some can eat this way for a lifetime and not have any heart-disease symptoms.

It isn’t a complete guessing game, though. Because radiation has been studied so much, there are some things we can say with certainty that apply to a majority of the population. We can say that for a small radiation dose (<10 rem), the risk of cancer is very small, too small to have any observable health impact in the population of the United States. We know that if the radiation dose is quite large and given in a short period of time, like the 1,000 rem in the chart above, it will cause an individual to be very sick and die.

Let’s Learn More about the Effects of Radiation

Let’s fill in the chart with a little bit more of what we know about getting a radiation dose to our entire body:

  • 0 - 5 rem received in a short period or over a long period is safe—we don’t expect observable health effects.
  • 5 - 10 rem received in a short period or over a long period is safe—we don’t expect observable health effects. At this level, an effect is either nonexistent or too small to observe.
  • 10 - 50 rem received in a short period or over a long period—we don’t expect observable health effects although above 10 rem your chances of getting cancer are slightly increased. We may also see short-term blood cell decreases for doses of about 50 rem received in a matter of minutes.
  • 50 - 100 rem received in a short period will likely cause some observable health effects and received over a long period will increase your chances of getting cancer. Above 50 rem we may see some changes in blood cells, but the blood system quickly recovers.
  • 100 - 200 rem received in a short period will cause nausea and fatigue. 100 - 200 rem received over a long period will increase your chances of getting cancer.
  • 200 - 300 rem received in a short period will cause nausea and vomiting within 24-48 hours. Medical attention should be sought.
  • 300 - 500 rem received in a short period will cause nausea, vomiting, and diarrhea within hours. Loss of hair and appetite occurs within a week. Medical attention must be sought for survival; half of the people exposed to radiation at this level will die if they receive no medical attention.
  • 500 - 1,200 rem in a short period will likely lead to death within a few days.
  • >10,000 rem in a short period will lead to death within a few hours.

The health effects listed above are for a radiation dose to the entire body. If the radiation is given to a smaller area of the body, there are other effects that may occur, but illness or death is not expected unless noted:

  • 40 rem or more locally to the eyes can cause cataracts.
  • 100 rem - 500 rem or more can cause hair loss for a section of the body that has hair.
  • 200 rem or more locally to the skin can cause skin reddening (similar to a sunburn).
  • 1,000 rem or more can cause a breakdown of the intestinal lining, leading to internal bleeding, which can lead to illness and death when the dose is to the abdomen.
  • >1,500 rem or more locally to the skin can cause skin reddening and blistering.