Which statement describes a stochastic effect?

• A. They have a threshold; severity increases with dose.
• B. They have no threshold; probability increases with dose.
• C. They occur only with internal contamination.
• D. They are independent of dose.

Answer: (B)

Stochastic effects are probabilistic in nature. They don’t have a defined dose where they start; instead, the likelihood of occurrence rises with increasing dose, especially at low doses where risk is proportional to exposure. The severity, once a stochastic effect occurs (like cancer), isn’t determined by how large the dose was—the chance of it happening grows with dose, not the seriousness of the outcome.

So the statement that best describes a stochastic effect is that there is no threshold and the probability of occurrence increases with dose. The other descriptions fit deterministic effects (which have a threshold and show more severe outcomes with higher dose), are not exclusive to internal contamination, or claim no dose dependence, which isn’t accurate for stochastic effects.