Lethality

Lethality is the property of a substance, process, or condition that is capable of causing death. In medicine, toxicology, and pharmacology, lethality is often quantified by a dose or concentration that kills a certain proportion of subjects, such as the LD50 (lethal dose for 50% of subjects) or the LC50 (lethal concentration). These measures enable comparisons of acute danger across chemicals and drugs, but they depend on species, route of exposure, and experimental conditions.

In infectious disease and epidemiology, lethality is represented by measures like the case fatality rate (the proportion of diagnosed cases that result in death) or the infection fatality rate (the proportion of all infections that result in death). Lethality refers more broadly to the likelihood that a given factor will cause death under specified conditions, including dose, age, health status, and environmental factors. It is related to, but distinct from, virulence (the capacity to cause disease) and contagion (the ability to spread).

Determinants of lethality include dose, exposure route, duration, host susceptibility, and the availability and quality of medical care. Lethality can be mitigated by interventions such as antidotes, supportive care, vaccination, and safety measures. It is a central parameter in risk assessment for chemicals, pharmaceuticals, pesticides, and engineered systems. Notable limitations of lethal metrics include species differences, non-linear dose–response relationships, and ethical constraints on human testing.