Toxicity refers to the degree to which a substance (chemical, drug, toxin, venom, pollutant, or even certain foods/plants) can cause harmful effects or damage to living organisms, ranging from mild irritation to severe organ failure or death. It is measured by factors like dose, route of exposure (ingestion, inhalation, skin contact, injection), duration (acute/single exposure vs. chronic/repeated), and individual susceptibility (age, health status, genetics). Common examples include drug toxicity (e.g., acetaminophen overdose causing liver failure, alcohol poisoning leading to respiratory depression), heavy metal toxicity (e.g., lead causing neurological damage, mercury affecting kidneys/brain), environmental toxins (e.g., carbon monoxide binding to hemoglobin and starving tissues of oxygen, pesticides causing neurological symptoms), venom toxicity (e.g., snake or spider bites with neurotoxic, hemotoxic, or cytotoxic effects), food-related (e.g., botulism toxin from improperly canned foods causing paralysis), and radiation toxicity (cellular/DNA damage from high doses). Symptoms vary widely by agent but often include nausea, vomiting, dizziness, confusion, seizures, organ-specific failure (liver, kidney, heart, lungs, nervous system), skin/mucous membrane burns, bleeding, or systemic shock; toxicity can be local (at site of contact) or systemic (widespread after absorption).