A toxin (Greek: τοξικόν, toxikon) is a poisonous substance produced by living cells or organisms (technically, although humans are living organisms, man-made substances created by artificial processes usually are not considered toxins by this definition). It was the organic chemist Ludwig Brieger (1849–1919) who first used the term 'toxin'.
For a toxic substance not produced by living organisms, "toxicant" is the more appropriate term, and "toxics" is an acceptable plural.
Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules such as enzymes or cellular receptors. Toxins vary greatly in their severity, ranging from usually minor and acute (as in a bee sting) to almost immediately deadly (as in botulinum toxin).
Toxins are often distinguished from other chemical agents by their method of production - the word toxin does not specify method of delivery (compare with venom and the narrower meaning of poison – all substances that can also cause disturbances to organisms). It simply means it is a biologically produced poison. There was an ongoing terminological dispute between NATO and the Warsaw Pact over whether to call a toxin a biological or chemical agent, in which the NATO opted for chemical agent, and the Warsaw Pact for biological agent.
According to a International Committee of the Red Cross review of the Biological Weapons Convention, "Toxins are poisonous products of organisms; unlike biological agents, they are inanimate and not capable of reproducing themselves." and "Since the signing of the Convention, there have been no disputes among the parties regarding the definition of biological agents or toxins..."
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