By Health.com
Updated May 01, 2008

We absorb radiation from a variety of sources. How much is too much? Experts say 3 mSv per year is probably OK for most of us; 20 mSv for those who must have medical tests.

*mSv=millisievert, the scientific unit of measurement for radiation dose. At high levels, radiation can mutate the structure (genetic components) of a body's dividing or reproducing cells and increase cancer risks. Sources: American College of Radiology; Radiological Society of North America; American Association of Physical Medicine; The New England Journal of Medicine; University of California, San Francisco, Cancer Center.