Every day, we are surrounded by radiation. We are constantly exposed to natural and man-made radiation sources, from the sunlight that warms our skin to the bananas we eat for breakfast. As a scientist, I have spent years researching various types of radiation, their sources, and their effects on human health.
In this article, I will describe the various types of radiation we encounter on a daily basis, where they come from, and how our activities contribute to the amount of radiation in our environment.
Radiation from Space
The earth and all living things on it are constantly bombarded with radiation from space. The sun is responsible for the majority of this extraterrestrial radiation. Nuclear fusion reactions deep within the sun’s core generate solar energy. This process produces gamma rays and highly energetic particles, which make up sunlight. Fortunately, much of the harmful radiation is absorbed or deflected by the earth’s protective gases and magnetic fields. We do, however, get exposed every time we step outside on a sunny day. From space, solar energy delivers around 10–15 millirems of radiation exposure annually at sea level. This exposure can vary depending on factors such as altitude and latitude.
In addition to bombarding us with photons, which determine how we perceive the world around us, our sun also emits neutrinos. Neutrinos are constantly passing through your body at a rate of nearly 100 trillion per second, without interacting with matter. These subatomic particles are so tiny and weakly interacting that they can easily pass through the Earth without being affected.
Besides the sun, supernovas, pulsars, black holes, and other cosmic events occurring light years away emit cosmic radiation that travels through space to reach Earth. Thankfully, the earth’s atmosphere absorbs most high-energy cosmic particles before they impact living organisms. However, airline crew and frequent fliers do face slightly higher risks associated with prolonged cosmic radiation exposure at the typical cruising altitudes of commercial jets. In fact, airline crews may absorb 2–5 millirems per hour of cosmic rays.
Radiation is not limited to the extraterrestrial world. The ground beneath our feet contains radioactive isotopes generated by the disintegration of uranium and thorium, naturally found in soils, rocks, and minerals.
In most locations, concentrations are low enough that exposure poses minimal risks. However, certain areas considered “radiation hotspots” have significantly higher levels, usually tied to local geology. The Pocos de Caldas plateau in Brazil, Ramsar in Iran, Guarapari Beach in Brazil, and Kerala in India boast exceptionally high background radiation from the surrounding mineral-rich terrain.
According to the latest measurements, terrestrial sources contribute roughly 60 millirems per year, escalating to over 500 millirems in extreme geological hotspots globally.
In addition to radiation emitted by the earth’s crust, we produce our own share of “civilization” radiation by harnessing the power of the atom for nuclear energy production, warfare, medicine, and other purposes. Average people generate nearly one-third of their exposure from medical radiation for health analysis and treatment. A single CT scan delivers 100 millirems, while nuclear imaging often exceeds 25 millirems per test.
Furthermore, nuclear disasters such as Chernobyl and Fukushima have shown how, when things go wrong, human technology can cause unintended environmental contamination. There are over 400 active nuclear reactors worldwide, with approximately 2,500 storage facilities housing highly radioactive spent fuel.
Radiation in the Food We Eat
Radiation also hides in the food we eat! Radioactive isotopes of potassium, carbon, and other elements are naturally incorporated into plants as they grow. Naturally occurring radionuclides in bananas and other foods provide around 35 millirems of intake per year.
In the 1950s, producers began irradiating fruits, spices, meat, and poultry to control microbial growth, providing another source of food-based radiation. Food irradiation uses gamma rays, X-rays, or electron beams to break DNA bonds within bacteria and fungi, killing or inactivating these pathogens before packaging and distribution.
Irradiated meat now accounts for approximately 35% of ground beef and precooked meals sold in supermarkets. Typically, irradiated meat may contain low residual doses under 5 millimetres.
Even on the most technologically sterile desert island, we humans still produce our own unique radiation signature from the food we eat.
In fact, our body is a small-scale mine of radioactive particles. Our bodies naturally contain radioactive potassium-40 and carbon-14 courtesy of ongoing metabolic processes. They get absorbed into your molecules and eventually decay, emitting radiation in your body.
When potassium-40 decays, it emits a positron, the electron’s antimatter twin, so you contain some antimatter as well. The average person generates over 4000 positrons per day, or about 180 per hour. But it won’t be long before these positrons collide with your electrons and annihilate into gamma-ray radiation.
The natural radioactivity that originates within you provides around 40 millirem dose every year. That’s the same amount of radiation you’d get from four chest X-rays. In addition, for every eight hours you spend sleeping next to a similarly radioactive loved one, your radiation dose level can rise by one or two millirem.
Every year, people are exposed to an estimated 620 millirems of radiation. While high levels cause tissue damage, modern science suggests that acute problems are unlikely below 5 Rem (5000 millirem), with cancer risks potentially increasing above a cumulative dosage of 15 Rem.
One sievert equals 100 rem. (1 Sv = 100 rem). One milliSievert equals one hundred millrems (1 mSv = 100 millrems).
- United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). UNSCEAR 2017 Report to the General Assembly. 2017.
- World Health Organisation (WHO). Ionising Radiation, Health Effects, and Protective Measures. 2016.
- Environmental Protection Agency (EPA). Radiation Protection Basics. Retrieved from https://www.epa.gov/radiation/radiation-basics
- Centres for Disease Control and Prevention (CDC). What is food irradiation? Retrieved from https://www.cdc.gov/features/foodirradiation/index.html
- National Academy of Sciences, Engineering, and Medicine 2021. The Biological Effects of Ionising Radiation: BEIR VII Phase 2. Washington, DC: The National Academies Press. https://doi.org/10.17226/24675