Regulations and guidelines of the US Nuclear Regulatory Commission (NRC) are based on the assumption that any amount of ionizing radiation, no matter how small, can have a harmful effect on an adult, child, or unborn child. This assumption is conservative, because there are no data showing ill effects from small dosages.
For small doses of radiation exposure, estimates of the significance of risks are quite inaccurate. For doses less than 10 mSv , the risk is too small to measure. For doses 10 to 50 mSv, the risk may be similar to other every day risks, such as driving a car. On the other hand, for radiation exposure exceeding 50 mSv, there is a measurable and significant increase in cancer risk; the magnitude of the risk varies widely, depending on the part of the body receiving the radiation. Thus, research involving radiation exposure of 50 or more mSv would be justifiable only if there is strong likelihood that the subject will benefit from the exposure directly, and if the expected benefits clearly outweigh the risks.