A toxin is a poisonous substance that is produced by living cells or organisms and is capable of causing disease when introduced into the body tissues but it's also capable of inducing neutralizing antibodies or antitoxins. Toxins can be small molecules, peptides or proteins. Toxins vary greatly in their severity, ranging from usually minor and acute e. g. in a bee sting to almost immediately deadly like those produced by some snakes.
Attribution: Straight Talk Foundation