The short answer
Cosmic radiation comes from the sun and stars, and EPA says the amount generally increases with elevation. Someone in Denver receives a higher annual cosmic dose than someone at sea level. EPA also states that low-level environmental radiation causes a small increase in lifetime cancer risk and is a minor contributor to overall cancer risk.
Cosmic radiation is made of energetic particles from the sun and stars that enter Earth's atmosphere.
EPA says the amount of cosmic radiation generally increases with elevation.
EPA gives Denver, at 5,280 feet, as an example of a higher annual cosmic dose than sea level.
The average American receives 6.2 millisieverts, or 620 millirem, per year from all sources.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
Yes, altitude changes your dose
This page is for people who live at high elevation and wonder about radiation and cancer. It explains what changes with altitude and how big that change is.
This one has a real physical basis, unlike many exposure worries. Cosmic radiation is made of very high-energy particles from the sun and stars. They enter Earth's atmosphere. Some reach ground level. Others interact with the atmosphere on the way down and produce other kinds of radiation.
The atmosphere is doing shielding work. The higher you live, the less of it sits above you. EPA puts it simply: radiation levels increase as you get closer to the source, so the amount of cosmic radiation generally increases with elevation.
EPA's own example is Denver, at 5,280 feet, where residents receive a higher annual dose from cosmic radiation than someone living at sea level.
Now the part that gives it scale
An increase is only meaningful once you know what it is an increase within.
Background radiation is present on Earth at all times. Most of it comes from naturally occurring minerals in soil and water, with a small fraction from human activities. Using data EPA cites from the National Council on Radiation Protection and Measurements (NCRP), the average American receives 6.2 millisieverts, or 620 millirem, per year from all sources combined.
Within that total, one source dominates for most people. Radon in average U.S. homes contributes roughly 2.28 millisieverts per year, making it the largest single contributor.
The gas that may be seeping into your basement typically matters more than the mountain you live on.
What EPA says about the risk itself
EPA is clear about how low-dose exposure behaves. Exposure to low levels of radiation does not cause immediate health effects, but can cause a small increase in the risk of cancer over a lifetime. The agency also states that low-level environmental radiation is a minor contributor to our overall cancer risk.
Why is it treated as a risk at all, rather than as harmless? The answer comes from the model EPA uses for setting limits. Under the linear no-threshold model, risk is assumed to rise in step with dose, with no safe threshold. So cutting the dose in half cuts the risk in half. EPA says the National Academy of Sciences and the NCRP have endorsed this approach.
The model assumes no dose is completely without risk.
A sense of scale
EPA notes that at 100 millisieverts from a single exposure, about 99 percent of people would not develop cancer from a single whole-body exposure. EPA adds that excess cancers at that dose are hard to detect against the baseline rate.
What to actually do with this
If you live somewhere high and this has been bothering you, the practical response is not relocation. It is to spend the concern where it buys you more.
- Ask about testing your home for radon, since it is the largest single source in EPA's figures.
- Keep a rough record of medical imaging, and ask whether a scan is needed and whether a lower-dose option exists.
- Altitude is a fixed part of where you live. EPA's figures put the biggest source inside the home.
Common questions
Am I getting more radiation because I live in the mountains?
EPA says cosmic radiation generally increases with elevation, and gives Denver at 5,280 feet as an example of receiving a higher annual cosmic dose than sea level.
Does that mean my cancer risk is higher?
EPA's framing of low-level radiation is that exposure does not cause immediate health effects but can cause a small increase in the risk of cancer over a lifetime, and that it is a minor contributor to overall cancer risk.
What is the biggest radiation source for most people?
According to the figures EPA cites, radon in average U.S. homes contributes about 2.28 millisieverts per year, the largest single source for most people.
Should I move to a lower elevation?
This page found no EPA advice to move. EPA's figures put radon in an average home (2.28 millisieverts a year) well above what this page cites for altitude. Ask your care team about your own situation.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Your next step
Turn this topic into questions for your next appointment.
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-08-11
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.