How many bananas would it take to be dangerous?

Bananas don't build up radiation in your body, because the body keeps potassium steady and gets rid of the extra. About 100 bananas equal one ordinary day of natural background radiation in the US.

What is the banana equivalent dose?

An informal unit of about 0.1 microsieverts, the dose often credited to eating one banana. Scientists use it to make tiny radiation amounts easier to picture.

Food Stories · Episode 4 · Why does...?

Are Bananas Radioactive? The Banana Equivalent Dose, Explained

Name: Are bananas radioactive?
Uploaded: 2026-10-13T06:44:33-07:00
Duration: 1 min 40 s
Description: Bananas contain a tiny amount of radioactive potassium-40, and so do you. Why it's harmless, what the banana equivalent dose is, and which foods have more.

Bananas contain a tiny amount of radioactive potassium-40, and so do you. Why it's harmless, what the banana equivalent dose is, and which foods have more.

The short answer

Yes, a tiny bit. Bananas are rich in potassium, and a small fraction of all potassium is the radioactive form potassium-40. One banana gives about 0.1 microsieverts, and you would need to eat about 100 bananas to match the natural background radiation a person in the United States gets each day. Your body keeps its potassium level steady, so bananas don't build up radiation inside you.

All plants and animals, including people, contain some potassium-40.
The banana equivalent dose (about 0.1 microsieverts) is an informal comparison unit.
Carrots and potatoes have almost as much potassium-40 as bananas; lima beans and Brazil nuts have more.
The EPA says these foods do not pose a radiation risk.

The story (transcript)

Narration from the episode, as it is spoken.

You pack a banana in your lunch. Guess what? It's a tiny bit radioactive.

Wait. Radioactive? Should you be worried?

Bananas have lots of potassium, and your body needs potassium. But a teeny fraction of all potassium is a radioactive kind, called potassium forty.

It's not just in bananas. All plants and animals have a little potassium forty. That includes you.

Scientists even use a joke unit for tiny amounts of radiation: the banana equivalent dose. One banana gives you about zero point one microsieverts.

That is tiny. You'd have to eat about one hundred bananas to match the radiation people in the United States get from nature every single day.

And here's the twist. Bananas don't pile up radiation inside you. Your body keeps its potassium level steady, so the extra goes out in your pee, almost right away.

Bananas aren't even the champions. Carrots and potatoes have almost as much potassium forty. Lima beans have more. And Brazil nuts have more still, plus some radium.

Fun fact to share at lunch: you are a little bit radioactive too, and that's totally normal.

Brought to you by Wonderade, the juice you wish you had when you were growing up.

Questions people ask

Are bananas radioactive?: Slightly. They contain potassium, and a small fraction of potassium is radioactive potassium-40. The EPA says this does not pose a radiation risk.
How many bananas would it take to be dangerous?: Bananas don't build up radiation in your body, because the body keeps potassium steady and gets rid of the extra. About 100 bananas equal one ordinary day of natural background radiation in the US.
What is the banana equivalent dose?: An informal unit of about 0.1 microsieverts, the dose often credited to eating one banana. Scientists use it to make tiny radiation amounts easier to picture.

Sources

Each source is listed with the facts we took from it.

A small fraction of all potassium is radioactive; one banana gives about 0.01 millirem (0.1 microsieverts); about 100 bananas equal the dose a person in the United States gets each day from natural environmental sources; these foods "do not pose a radiation risk" · U.S. EPA RadTown, "Natural Radioactivity in Food": https://www.epa.gov/radtown/natural-radioactivity-food
"All organic matter (both plant and animal) contains some small amount of radiation from radioactive potassium-40"; K-40 per kg: bananas 3,520 pCi, carrots 3,400, white potatoes 3,400, raw lima beans 4,640, Brazil nuts 5,600 (plus 1,000-7,000 pCi/kg radium-226); average internal dose from food and water about 30 millirem per year · U.S. Nuclear Regulatory Commission, "Doses in Our Daily Lives": https://www.nrc.gov/about-nrc/radiation/around-us/doses-daily-lives.html
Banana equivalent dose is a "fake unit" of about 0.1 microsievert; excess potassium is excreted in urine almost immediately, so eating bananas has practically no effect on the dose you actually receive · University of Groningen, Radiation Protection A-Z, "Banana equivalent dose": https://www.rug.nl/education/courses/other-education/radiation-protection/a-z/a-z-data/banana-equivalent-dose

How we checked this

What we simplified, hedged or left out, and why.

0.1 microsievert is a rounded, informal number. Calculations range about 0.08-0.1 µSv depending on the dose coefficient used; EPA states 0.1. The narration says "about".
"About one hundred bananas a day of nature" is EPA's comparison for the U.S. average, so the narration says "people in the United States".
The twist is the honest core. Because the body holds potassium steady (homeostasis), a banana barely changes your actual internal dose; the "banana dose" is a comparison yardstick, which the narration calls "a joke unit".
"Almost right away" follows the Groningen wording ("bijna onmiddellijk"). It is a simplification of the kidneys restoring balance over hours.
Brazil nuts. NRC lists more K-40 per kg and far more radium than bananas. "Some radium" makes no safety claim either way.
Cut on purpose. The popular story that banana shipments set off port radiation detectors is disputed (other sources say ceramics and clay litter, not bananas, are the usual triggers), so it is left out.