Which statement about threshold dose is true?

• A. Stochastic effects have a threshold.
• B. Nonstochastic effects have no threshold.
• C. Stochastic effects have no threshold; nonstochastic have a threshold.
• D. Both types lack a threshold.

Answer: (C)

Threshold dose is about whether a health effect appears only above a certain dose. For radiation effects, the distinction between stochastic and nonstochastic outcomes matters here.

Nonstochastic (deterministic) effects require a minimum amount of radiation before they occur, and their severity increases with dose once you pass that threshold. Examples include skin erythema or cataracts at high doses. Stochastic effects, like cancer or genetic changes, are probabilistic: there’s no known safe lower limit, and the chance of occurrence rises with dose, but the severity isn’t tied to the dose in the same way.

So the true statement is that stochastic effects have no threshold, while nonstochastic effects do have a threshold. The other options misstate this relationship.