Which term describes biological effects with a threshold dose and a clear dose–response relationship?

• A. Nonstochastic effects
• B. Stochastic effects
• C. Genetic effects
• D. Deterministic effects

Answer: (A)

Deterministic effects, also called nonstochastic effects, require a threshold dose and show a clear, predictable rise in severity as the dose increases above that threshold. Below the threshold, no effect is observed; once crossed, higher doses produce more severe outcomes. This is why the correct term is nonstochastic: it denotes those dose–response relationships where severity scales with dose once the threshold is exceeded. Examples include skin reddening, hair loss, radiation sickness, and cataracts at sufficient doses—each has a defined threshold. In contrast, stochastic effects (like cancer or genetic effects) have no true threshold—the probability of occurrence increases with dose, but the severity is not dose-dependent.