Although the biological effects of large doses of ionizing radiation are predominantly harmful, low-to-intermediate doses have been observed to enhance growth and survival, augment the immune response, and increase resistance to the mutagenic and clastogenic effects of further irradiation in plants, bacteria, insects, and mammals. The existence of these stimulatory, or "adaptive", responses implies that the dose-response relationships for genetic and carcinogenic effects of radiation may be similarly biphasic, or hormetic, in nature, a possibility with far-reaching implications for radiation protection. As yet, however, the extent to which such responses may actually reduce the risks attributable to low-level irradiation remains to be determined, pending further elucidation of the relevant dose-response relationships and the apparent lack of responsiveness in some individuals. Therefore, further research is needed to resolve this question.

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