September 06, 2001

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.

CT scan, full body
10–12 mSv
CT scan, chest or pelvis
4–8 mSv
Natural background radiation (from sunlight, radon gas, etc.) from living in high-altitude cities (e.g., Denver, Salt Lake City)
6 mSv (per year)
Natural background radiation from living at sea level (e.g., Chicago)
3 mSv (per year)
1–2 mSv
High-mileage frequent flying (100,000–450,000 miles per year)
1–6.7 mSv
X-ray of chest (or ankle to look for broken bones)
0.1–0.6 mSv
DEXA (bone-density) scan
0.01–0.05 mSv
Dental X-ray (bitewing)
0.02 mSv
Single airplane flight, coast-to-coast
0.01–0.03 mSv

*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.