According to the Nuclear Regulatory Commission, about half of the radiation we encounter every year comes from background radiation, or ubiquitous radiation that reaches everyone on earth. You don’t have to go near a nuclear plant or get an X-ray to receive a dose of radiation—these emissions can come from inconspicuous household items such as nuts, granite countertops, and smoke detectors. Oh, and also your own body.

1. Brazil nuts

Brazil nuts (especially the ones grown in Brazil) grow on trees with deep roots, which reach down to soil high in natural radium, a source of radiation. The roots absorb the radium, which then makes its way to the nuts. As a result, the radium levels of Brazil nuts can be 1000 times what you’d see in other foods. Luckily, the EPA regulates food radiation levels like these, so you should have a wide margin of error for safe snacking.

2. Bananas

You probably already knew that bananas are loaded with potassium. But bananas also happen to be one of the most radioactive foods because they contain the isotope potassium-40. Thanks to this isotope, everyone’s favorite yellow fruit emits a tiny amount of radiation. Much like the Brazil nuts, the radioactive potassium is taken up in the soil and absorbed by the fruit.

Bananas are such a common everyday source of radiation that there’s even an unofficial unit of measurement for radiation called the BED, or Banana Equivalent Dose, that’s used to illustrate foods’ radiation levels.

3. Your body

We encounter all sorts of radiation in day-to-day life, which in turn makes us a little radioactive. Because it’s commonly found in a number of foods, potassium-40 is the main source of radiation in our bodies, but our bodies also pick up radiation from the air we breathe and the water that we drink. The natural amount of radioactive carbon-14 present in your body is what enables archaeologists to determine age ranges for skeletons.

4. Smoke detectors

Some household smoke detectors use tiny amounts of a radioactive isotope, americium-241, to alert you when there’s smoke in the air. The material is surrounded by ceramic and foil, so it doesn’t pose any harm to you so long as you don’t go tinkering with the detector. (But even then, unless you ground it up and swallowed the powder, you’d probably be fine.)

5. Granite countertops

Granite naturally contains uranium and thorium, because those elements are found in the magma that solidified to make it. But the real concern is radon. The naturally-occurring uranium decays into radon, which is a gas. And just like you shouldn’t be breathing in the powdered contents of smoke detectors, radioactive gases can be inhaled and cause health issues. But as far as kitchen islands go, granite is a fairly safe choice—it’s not too porous, which means that more of that radon is kept inside, according to the EPA.

6. Your grandma’s dinnerware

Elements like uranium, thorium, and that ever-present potassium-40 were common in the glaze coating some ceramic dishes and pottery until the 1960s. Homer Laughlin China Company, which makes the brightly colored Fiestaware sets, used depleted uranium oxide for its red dishes and natural uranium for the white ceramic dishes before the entire line was discontinued in 1972. So retire your dinnerware or be particularly careful about using it to eat acidic foods, which can leach uranium away from the dishes.

7. Cigarettes

The radiation in cigarettes doesn’t come from the chemical additives smokers are warned about; it actually comes from the tobacco itself. In a process similar to how bananas and Brazil nuts become radioactive, tobacco plants can absorb radioactive elements such as radium, lead-210, and polonium-210 from some fertilizers used on crops.

How Worried Should We Be About All This Background Radiation?

Not very. There’s nothing you can do about background radiation—according to the Nuclear Regulatory Commission, the average American receives a dose of about 620 millirems of radiation each year—and it’s normal to find it in products like these. As long as you don’t eat your smoke detector, these small sources won’t hurt you (but it’s always a good idea to quit smoking).

All images courtesy of iStock.