One of the most widely known characteristics of radiation is its ability to damage living tissue. The amount of damage sustained increases with increased exposure. That life has existed on Earth for over 3.5 billion years, is evidence that limited amounts of radiation exposure will not have a major impact, and may be repaired. However, large doses of radiation can have a significant effect on health, and significant doses over time can cause delayed effects such as cancer. The rate at which the dose is received is significant.
Different people respond differently to the same radiation dose.
Health effects from radiation exposure are not unique and, consequently, cannot easily be correctly attributed to the cause. Extra health care provided to those who have received high radiation doses may either reduce or emphasise the effects of the radiation. In order to make a complete evaluation of the effects in a group exposed to radiation it is necessary to follow the whole group throughout their lives. In spite of this, a great deal is known about the effect of exposure to radiation, more than for most chemical toxins, for instance. Information regarding the effects is derived primarily from groups of individuals who have received high radiation doses, including survivors of the bombing of Hiroshima and Nagasaki.