Inapplicability For carcinogenic substances, theoretically NOAEL and LOAEL do not exist as there is no safe dose for the carcinogens. A linear no-threshold model is commonly used for illustrating the probability of cancer development from radiation. There is no<unk>  value at which stochastic health effects start emerging. Only for non-cancer health outcomes, there is an assumption of the presence of a safety margin below which no negative biological effect is expected. Inconsistency Most dose-response models are obtained from animal experiments out of ethical concerns. Therefore, the results might not be consistent with that of the human population. Individual differences also arise among people in terms of age, weight, gender, health status, etc. Thus, in most circumstances, the<unk>  serves as a reference to evaluate the probable outcome of a certain dosage of a substance for the general population, while great deviations might exist in special populations such as immunocompromised patients, pregnant women and young children. Incomprehensiveness The<unk>  is only a measure of acute toxicity since the drug or toxic substance investigated is administered at once. The consequence of long-term administration remains unknown. As the<unk>  is the measured minimal response, its accuracy heavily depends on the machinery used. It is possible that further refinement is needed. Furthermore, the<unk>  only reflects the dose required for a minimum detectable response but it should not be misunderstood that health effects are absolutely absent in the doses below the<unk> .
Threshold dose
Equivalent dose
Effective dose 
Reference dose
Form constant
Relative value unit
Relative biological effectiveness
Absolute threshold