What is the key difference between stochastic and nonstochastic effects regarding threshold dose?

• A. Stochastic effects have no threshold; nonstochastic effects have a specific threshold.
• B. Stochastic effects have a threshold; nonstochastic effects have no threshold.
• C. Both have thresholds.
• D. Neither has a threshold.

Answer: (A)

The key idea is how dose threshold differs between risk types. Stochastic effects are probabilistic—any amount of exposure carries some chance of occurrence, and that risk grows with dose, but there isn’t a specific dose below which the effect cannot happen. Nonstochastic (deterministic) effects, on the other hand, require a minimum amount of dose to appear; below that threshold nothing is seen, and above it the severity increases with dose. So the correct distinction is that stochastic effects have no threshold, while nonstochastic effects have a threshold. For example, cancer risk is considered stochastic, whereas effects like skin erythema are deterministic.