The mission of EPA’s Radiation Protection Program is to protect human health and the environment from unnecessary exposure to radiation. This page provides basic information about the health effects of radiation. EPA uses current scientific understanding of the health effects of radiation exposure to create protective standards and guidance. Related information in Spanish (Información relacionada en español).
Ionizing radiationIonizing radiationRadiation with so much energy it can knock electrons out of atoms. Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes. has sufficient energy to cause chemical changes in cells and damage them. Some cells may die or become abnormal, either temporarily or permanently. By damaging the genetic material (DNA) contained in the body’s cells, radiation can cause cancer. Fortunately, our bodies are extremely efficient at repairing cell damage. The extent of the damage to the cells depends upon the amount and duration of the exposure, as well as the organs exposed.
A very large amount of radiation exposure (acute exposureacute exposureExposure to an amount of radiation all at once or from multiple exposures in a short period of time. In most cases, a large acute exposure to radiation causes both immediate (see radiation sickness) and delayed effects (cancer or death).), can cause sickness or even death within hours or days. Such acute exposures are extremely rare.
Visit the U.S. Centers for Disease Control and Prevention (CDC) for more information about possible health effects of radiation exposure and contamination.
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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: chronic (long-term) and acute (short-term).
Chronic exposureChronic exposureContinuous or intermittent exposure to radiation over a long period of time. With chronic exposure, there is a delay between the start of the exposure and the observed health effect, such as cancer, benign tumors, cataracts, and potentially harmful genetic changes. is continuous or intermittent exposure to radiation over a long period of time. With chronic exposure, there is a delay between the exposure and the observed health effect. These effects can include cancer and other health outcomes such as benign tumors, cataracts, and potentially harmful genetic changes.
Low Levels of Radiation Exposure
Current science suggests there is some cancer riskriskThe probability of injury, disease or death from exposure to a hazard. Radiation risk may refer to all excess cancers caused by radiation exposure (incidence risk ) or only excess fatal cancers (mortality risk). Risk may be expressed as a percent, a fraction, or a decimal value. For example, a 1% excess risk of cancer incidence is the same as a 1 in a hundred (1/100) risk or a risk of 0.01. from any exposure to radiation. However, it is very hard to tell whether a particular cancer was caused by very low doses of radiation or by something else. While experts disagree over the exact definition and effects of “low dose,” U.S. radiation protection standards are based on the premise that any radiation dose carries some risk, and that risk increases directly with dose. This method of estimating risk is called the "linear no-threshold model (LNTLNTThe assumption that the risk of cancer increases linearly as radiation dose increases. This means, for example, that doubling the dose doubles the risk and that even a small dose could result in a correspondingly small risk. Using current science, it is impossible to know what the actual risks are at very small doses.)." The risk of cancer from radiation also depends on age, sex, and factors such as tobacco use.
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Acute health effects occur when large parts of the body are exposed to a large amount of radiation. The large exposure can occur all at once or from multiple exposures in a short period of time. Instances of acute effects from environmental sources are very rare. Examples include accidentally handling a strong industrial radiation source or extreme events like nuclear explosions. Learn about protecting yourself from radiation.
It takes a large radiation exposure — more than 75 rad radThe U.S. unit used to measure absorbed radiation dose (the amount of radiation absorbed by an object or person). The international equivalent is the Gray (Gy). One hundred rads are equal to 1 Gray.— in a short amount of time to cause acute health effects like radiation sicknessradiation sicknessA serious illness that can happen when a person is exposed to very high levels of radiation, usually over a short period of time.. (This level of radiation would be equivalent to an x-ray dose of 75,000 milliremmilliremThe millirem is the U.S. unit used to measure effective dose. One millirem equals 0.001 rem. The international unit is milliSievert (mSv).. For comparison, the average dose from an adult chest x-ray is about 4 millirem. See Radiation Sources and Doses for more information about radiation sources.)
Exposures between 5 and 10 rad usually result in no acute health effects. However, exposures in this range slightly increase the risk of getting cancer in the future.
View CDC Fact Sheet: Acute Radiation Syndrome (ARS).
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Understanding the type of radiation received (alphaalpha particleA form of particulate ionizing radiation made up of two neutrons and two protons. Alpha particles pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled., betabeta particleA form of particulate ionizing radiation made up of small, fast-moving particles. Some beta particles are capable of penetrating the skin and causing damage such as skin burns. Beta-emitters are most hazardous when they are inhaled or swallowed., gammagamma raysA form of ionizing radiation that is made up of weightless packets of energy called photons. Gamma rays can pass completely through the human body; as they pass through, they can cause damage to tissue and DNA., x-rayx-raysA form of ionizing radiation made up of photons. X-rays are capable of passing completely through the human body. Medical x-rays are the single largest source of man-made radiation exposure.), the way a person is exposed (external vs. internal), and for how long a person is exposed are all important in estimating health effects.
The risk from exposure to a particular radioactive element depends on:
The risk that exposure to a radioactive element will cause a particular health effect also depends on whether exposure is internal or external.
- Internal exposure is when radioactive material gets inside the body by eating, drinking, breathing or injection (from certain medical procedures). Alpha and beta particles pose a serious health threat if significant quantities are inhaled or ingested. Outside the body, alpha particles are too large to pass through the skin or a thin layer of clothes.
- External exposure (also known as direct exposure) is when the radioactive source is outside of your body. X-rays and gamma rays can pass through your body, depositing energy as they go.
Learn more about alpha particles, beta particles, gamma rays and x-rays.
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Pregnant women and children are especially sensitive to radiation exposure. The cells in children and fetuses divide rapidly, providing more opportunity for radiation to disrupt the process and cause cell damage. EPA accounts for these differences in sensitivity due to age and sex when revising radiation protection standards.
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Ionizing radiation happens when the atomic nucleus of an unstable atom decays and starts releasing ionizing particles.
When these particles come into contact with organic material, such as human tissue, they will damage them if levels are high enough, in a short period of time. This can lead to burns, problems with the blood, gastrointestinal system, cardiovascular and central nervous system, cancer, and sometimes death.
Radiation is normally managed safely, but its use also entails a risk.
If an accident happens, for example, the earthquake in Fukushima, Japan, in 2011, or the explosion at Chernobyl, Ukraine in 1986, radiation can become dangerous.
Here are some key points about radiation poisoning. More detail is in the main article.
- Radiation is all around us and it is used safely in many applications.
- Nuclear accidents, the work environment, and some medical treatment can all be sources of radiation poisoning.
- Depending on the dose, the effects of radiation can be mild or life-threatening.
- There is no cure, but barriers can prevent exposure and some medications may remove some radiation from the body.
- Anyone who believes they have been exposed to radiation should seek medical attention as soon as possible.
What is radiation poisoning?
Radiation has many uses, but it can be dangerous if it is not managed correctly.
Radiation poisoning happens when a radioactive substance gives off particles that get into a person's body and cause harm. Different radioactive substances have different characteristics. They can harm and help people in different ways, and some are more dangerous than others.
Normally, radiation occurs in a safe environment. Whether or not it becomes dangerous depends on:
- how it is used
- how strong it is
- how often a person is exposed
- what type of exposure occurs
- how long exposure lasts
A dose of radiation from a single x-ray is not normally harmful. Nevertheless, the parts of the body that are not being x-rayed will be shielded with a lead apron to prevent unnecessary exposure.
The technician, meanwhile, will leave the room when taking the image. While one small dose is not dangerous, repeated small doses could be.
A sudden, short, low dose of radiation is unlikely to cause a problem, but extended, intense, or repeated doses can be. When radiation damages cells, it is irreversible. The more often a person is exposed, the greater their risk of health problems.
How much radiation is dangerous?
Radiation dosage can measured in various ways. Some of the units used are Grays, Sieverts, rems, and rads. They are used in a similarway, but 0.1 rad is equivalent to 100 Gray.
- Below 30 rads: Mild symptoms will occur in the blood
- From 30 to 200 rads: The person may become ill.
- From 200 to 1,000 rads: The person may become seriously ill.
- Over 1,000 rads: This will be fatal.
According to the Centers for Disease Control and Prevention (CDC), radiation sickness, or acute radiation syndrome (ARS) is diagnosed when:
- A person receives over 70 rads from a source outside their body
- The dose affects the whole body, or most of it, and is able to penetrate to the internal organs
- The dose is received in a short time, usually within minutes
A person who experiences an atomic explosion will receive two doses of radiation, one during the explosion, and another from fallout, when radioactive particles float down after the explosion.
Radiation sickness can be acute, happening soon after exposure, or chronic, where symptoms appear over time or after some time, possibly years later.
The signs and symptoms of acute radiation poisoning are:
- vomiting, diarrhea, and nausea
- loss of appetite
- malaise, or feeling unwell
- rapid heartbeat
Symptoms depend on the dose, and whether it is a single dose or repeated.
A dose of as low as 30 rads can lead to:
- loss of white blood cells
- nausea and vomiting
A dose of 300 rads dose may result in:
- temporary hair loss
- damage to nerve cells
- damage to the cells that line the digestive tract
Stages of radiation sickness
Symptoms of severe radiation poisoning will normally go through four stages.
Prodomal stage: Nausea, vomiting, and diarrhea, lasting from a few minutes to several days
Latent stage: Symptoms seem to disappear, and the person appears to recover
Overt stage: Depending on the type of exposure, this can involve problems with the cardiovascular, gastrointestinal, hematopoietic, and central nervous system (CNS)
Recovery or death: There may be a slow recovery, or the poisoning will be fatal.
Hematopoietic stem cells, or bone marrow cells, are the cells that all other blood cells derive from.
Different doses, different effects
The risk of illness depends on the dose. Very low doses of radiation are all around us all the time, and they do not have any effect. It also depends on the area of the body that is exposed.
If the whole body is exposed to, say, 1,000 rads within a short time, this could be fatal. However, far higher doses can be applied to a small area of the body with less risk.
After a mild dose, the person may experience symptoms for just a few hours or days. However, a repeated or even a single, relatively low dose that produces few or no visible symptoms around the time of exposure may cause problems later on.
A person who is exposed to 3,000 rads will experience nausea and vomiting, and they may experience confusion and a loss of consciousness within a few hours. Tremors and convulsions will occur 5 to 6 hours after exposure. Within 3 days, there will be coma and death.
People who experience repeated doses, or who appear to recover, may have long-term effects.
- a loss of white blood cells, making it harder for the body to fight infection
- reduction in platelets, increasing the risk of internal or external bleeding
- fertility problems, including loss of menstruation and reduced libido
- changes in kidney function, which can lead to anemia, high blood pressure, and other problems within a few months
There may also be skin redness, cataracts, and heart problems.
Localized exposure may lead to changes in the skin, loss of hair, and possibly skin cancer.
Exposure to certain parts of the body is more dangerous than others, for example, the intestines.
The effects of radiation are cumulative. Damage to cells is irreversible.
Exposure to radiation can result from workplace exposure or an industrial accident, radiation therapy, or even deliberate poisoning, as in the case of the former Russian spy, Alexander Litvinenko, who was murdered in London by polonium 210 placed in his tea. However, this is extremely rare.
CT scans should only be carried out when necessary, as they expose a person to more radiation than is usual in everyday life.
Most people are exposed to an average of around 0.62 rads, or 620 Gray each year.
Half of this comes from radon in the air, from the Earth, and from cosmic rays. The other half comes from medical, commercial, and industrial sources. Spread over a year, this is not significant in terms of health.
Levels of radiation from an x-ray are not high, but they occur at one moment.
- A chest x-ray gives the equivalent of 10 days' exposure to radiation
- Mammogram gives the equivalent of 7 weeks' normal exposure
- PET or CT used as part of nuclear medicine exposes a person to the equivalent of 8 years of radiation
- A CT scan of the abdomen and pelvis gives the equivalent of 3 years' normal exposure
Nuclear medicine is used to target the thyroid in people with a thyroid disorder. Other types of medical treatment include radiation therapy for cancer.
Living at a higher altitude, for example, in the plateau of New Mexico and Colorado, increase exposure, as does traveling in an airplane. Radon gas in homes also contributes.
Food, too, contains small amounts of radiation. The food and water we drink is responsible for exposure to around 0.03 rads in a year.
The many activities that can expose people to sources of radiation include:
- watching television
- flying in an airplane
- passing through a security scanner
- using a microwave or cell phone
Smokers have a higher exposure than non-smokers, as tobacco contains a substance that can decay to become polonium 210.
Astronauts have the highest exposure of anyone. They may be exposed to 25 rads in one Space Shuttle mission.
Damage by radiation is irreversible. Once the cells are damaged, they do not repair themselves. Until now, there is no way for medicine to do this, so it is important for someone who has been exposed to seek medical help as soon as possible.
Possible treatments include:
- Removing all clothing,
- Rinsing with water and soap.
- Use of potassium iodide (KI) to block thyroid uptake if a person inhales or swallows too much radioiodine
- Prussian blue, given in capsules, can trap cesium and thallium in the intestines and prevent them from being absorbed. This allows them to move through the digestive system and leave he body in bowel movements.
- Filgrastim, or Neupogen, stimulates the growth of white blood cells. This can help if radiation has affected the bone marrow.
Depending on exposure, radiation can affect the whole body. For cardiovascular, intestinal, and other problems, treatment will target the symptoms.
Reducing exposure to radiation
Tips for reducing unnecessary exposure to radiation include:
- keeping out of the sun around midday and using a sunscreen or wearing clothes that cover the skin
- making sure any CT scans and x-rays are necessary, especially for children
- letting the doctor know if you are or may be pregnant before having an x-ray, PET, or CT scan
It is not possible or necessary to avoid all exposure to radiation, and the risk posed to health by most sources is extremely small.