A toxin is a poisonous substance, and in careful scientific use it means a poison made by a living thing — bacteria, a fungus, a plant, a snake, a jellyfish. That is the difference science draws: a toxin is a poison of biological origin, while a poison made in a factory is usually called a toxic chemical or just a poison. Food poisoning is the everyday example: some bacteria in badly stored food release toxins, and it is those toxins, not the bacteria themselves, that make you vomit. Two toxins you may have heard of are botulinum toxin, the strongest one known, which in tiny doses is sold as Botox, and the tetanus toxin, which is what the vaccine protects you against. Now the messy truth: outside science, people use toxin very loosely. Advertisements for teas, foot patches, and 'detox' programmes promise to remove 'toxins' from your body without ever naming one, and this vague use is mostly marketing rather than medicine. Your liver and kidneys already do that work. So when you read 'toxin', it is worth asking which toxin is meant — a real named substance, or a word used to sound scientific.