Radiation is present throughout the universe. The decay of atoms is called radioactivity. Radiation is the energy produced by this decay, and the type that is dangerous to us is ionizing radiation. When the electrical ions produced by this decay pass through living tissue, they can influence biological functions [source: IAEA].
Ever since humans first appeared, we've been bombarded by radiation from outer space and exposed to radioactive materials in the Earth itself. Scientists estimate that about 80 percent of the radiation we're exposed to comes from natural sources. While those are by far the most common sources of radiation, they are not the ones that worry most people. We're concerned about the impact of medical scans, X-rays and radiation therapy. These procedures account for about 15 percent of our exposure to radiation [source: HPS]. The remainder comes from lesser sources such as glow-in-the-dark watch faces, microwave ovens, cell phones and even antique glass.
Some of our fears about exposure to radiation are justified. Others can be dismissed. In this article, we'll examine some common sources of radiation and see what we can do to keep ourselves safe.