Radiation hormesis is often presented in isolation, but it only makes sense when viewed alongside the other dose–response models used in radiation science.
These models attempt to describe how radiation dose relates to cancer risk. They are not all equally supported, and they are not all used in practice.
The linear no-threshold model assumes that:
This model is used by major organisations, including the International Commission on Radiological Protection (ICRP), and underpins radiation safety standards worldwide.
It is based on epidemiological data at moderate to high doses, with a conservative extrapolation to low doses (National Research Council, 2006; ICRP, 2007).
The linear–quadratic model describes how biological damage increases with dose using both linear and quadratic components.
This model is well established in radiobiology and widely used in radiotherapy to model cell survival and tissue response (Hall & Giaccia, 2019).
It is not primarily used for population cancer risk, but it is important for understanding the cellular effects of radiation.
Hormesis proposes a different type of response:
In this model, the curve dips below baseline risk at low doses before rising at higher exposures.
Some laboratory studies show:
However, human evidence is inconsistent, and results are not reliable enough to support clinical or regulatory use (Calabrese & Baldwin, 2003; UNSCEAR, 2010).
The threshold model suggests:
This is often represented as a sigmoid or “S-shaped” curve.
While biologically plausible, there is no clear, consistent evidence defining a safe threshold in human populations exposed to ionising radiation (Little et al., 2009).
Only LNT is currently used for radiation protection policy.
Radiation protection is based on population safety, not individual variability.
LNT is used because:
Even if adaptive responses exist at low doses, they are not predictable or uniform across individuals.
In practice, nothing changes:
Students and professionals should understand all models, but apply LNT in decision-making.
Hormesis is one of several models used to describe radiation effects. While it has experimental support, it remains unproven in human populations.
Radiation protection continues to rely on the linear no-threshold model because it provides a consistent and precautionary approach to managing risk.
What is radiation hormesis?
A proposed response where low doses of radiation may produce adaptive or beneficial effects, while higher doses are harmful.
Are all radiation dose models equally accepted?
No. Only the linear no-threshold model is used in radiation protection.
What is the linear–quadratic model used for?
It is used in radiobiology and radiotherapy to model cellular response to radiation.
Is there a safe threshold for radiation exposure?
There is no clearly established safe threshold in human populations.
Why is LNT still used?
Because it provides a conservative and consistent approach to managing radiation risk.
Calabrese, E. J., & Baldwin, L. A. (2003). Hormesis: The dose-response revolution. Annual Review of Pharmacology and Toxicology, 43, 175–197. https://doi.org/10.1146/annurev.pharmtox.43.100901.140223
National Research Council. (2006). Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. National Academies Press. https://doi.org/10.17226/11340
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). (2010). Sources and effects of ionizing radiation. United Nations.
International Commission on Radiological Protection (ICRP). (2007). ICRP Publication 103: The 2007 Recommendations of the International Commission on Radiological Protection. Annals of the ICRP, 37(2–4).
Little, M. P., Wakeford, R., Tawn, E. J., Bouffler, S. D., & Berrington de González, A. (2009). Risks associated with low doses and low dose rates of ionizing radiation: Why linearity may be (almost) the best we can do. Radiology, 251(1), 6–12. https://doi.org/10.1148/radiol.2511080671