A toxin (Greek: τοξικόν, toxikon, lit. (poison) for use on arrows) is a poisonous substance produced by living cells or organisms that is active at very low concentrations. Toxins can be small molecules, peptides, or proteins and are capable of causing disease on contact or absorption with body tissues by 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 its method of production- the word toxin does not specify method of delivery (compare with venom and (the narrower meaning) of poison). It simply means it is a biologically produced poison. There was an ongoing dispute between NATO and the Warsaw Pact over whether to call a toxin a biological or chemical agent, in which the former opted for the latter, and vice versa.
Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snail contains dozens of small proteins, each targeting a specific nerve channel or receptor), or relatively small protein.
Biotoxins in nature have two primary functions:
Some of the more well known types of biotoxins include:
In the context of alternative medicine the term is often used non-specifically to refer to any substance claimed to cause ill health, ranging anywhere from trace amounts of pesticides to common food items like refined sugar or additives like artificial sweeteners and MSG.