Look a little closer
Bananas are rich in potassium, and a tiny fraction of that potassium exists as the naturally occurring radioactive isotope potassium-40. That means eating a banana exposes you to an extremely small amount of radiation.
For this reason, scientists sometimes use a playful unit called the "banana equivalent dose," comparing the strength of other radiation sources to the amount of radiation exposure from eating a single banana.
There's absolutely nothing to worry about, though. The radiation dose from one banana is far too small to have any effect on the human body, and our bodies already naturally contain radioactive substances, including potassium-40, at all times.
The cosmic radiation received during a high-altitude airplane flight, or the dose from a single X-ray, is vastly greater than what you'd get from eating thousands of bananas. Banana radioactivity is a fun bit of science trivia, not something to worry about in everyday life.
