Bananas are mildly radioactive.

Potassium is essential to human biology, and a small, constant fraction of all naturally occurring potassium is potassium-40, a radioactive isotope. Since bananas are unusually rich in potassium, they emit a small amount of radiation — far too little to pose any health risk.

The dose is so small that physicists coined the informal unit “banana equivalent dose” to help explain radiation levels to non-specialists: eating one banana exposes you to roughly the same tiny dose as a few hours of ordinary background radiation.