The DEXA scan uses a tiny dose of ionising radiation (X-rays) to measure your body composition. To put the dose and the risk in perspective, it is equivalent to eating 50 grams of Brazil nuts, and less than one day’s normal background radiation that we each receive every day from outer space and the earth’s natural radiation.
To put it another way, you are effectively having a DEXA body scan every day without even knowing it. The dose is so low that the Care Quality Commission describes the risk from the radiation dose of a body scan as “negligible”. This chart shows dose comparisons (a DEXA bodyscan is the same as a dental X-ray, at 0.005mSv).
If you want more detail, please watch this video: