Harm caused by a single exposure or by multiple exposures within a short period, typically 24 hours, to a dose of a substance high enough to make a person seriously ill or kill. Toxicologists quantify it with measures such as the LD50, the dose lethal to half of test animals, and classify chemicals into hazard categories that determine warning labels and handling rules. In food safety, acute toxicity separates immediate poisoning risks, such as a massive dose of a pesticide residue or a potent natural toxin like tetrodotoxin, from chronic risks that build over years of low exposure. Regulatory limits for contaminants consider both: acute reference doses guard against single-meal poisoning, while tolerable daily intakes address lifetime exposure. Understanding this distinction keeps risk communication honest about what a single incident can and cannot do.