Toxins

A toxin is a poisonous substance produced by living organisms that can harm other organisms, typically by disrupting normal biological processes. In toxicology, toxins are distinguished from toxicants, which are toxic substances of non-biological origin or synthetic chemicals. Toxins can be proteins, peptides, or small molecules, and their effects depend on dose, route of exposure, and the biology of the target.

Toxins originate from bacteria, plants, animals, and fungi. Examples include botulinum toxin and diphtheria toxin from bacteria; ricin from castor beans; saxitoxin from certain algae; and spider or snake venoms that deliver toxins through bites or stings. Some toxins act by inhibiting protein synthesis, blocking ion channels, or damaging cell membranes and organ systems.

Mechanisms vary: enzymatic inhibition (for example, diphtheria toxin inhibits protein synthesis), neurotoxic effects that disrupt nerve signaling, or cytotoxic effects that kill cells. Toxicity is often quantified by metrics such as the LD50, and a substance may be highly potent in one species or exposure route but less so in another.

Exposure occurs through ingestion, inhalation, dermal contact, or injection. Medical response focuses on removing or neutralizing the toxin when possible, providing supportive care, and using antidotes or antitoxins for specific toxins. Vaccines based on toxoids — inactivated forms of toxins — can prevent disease for some toxins.

In addition to health risks, toxins have roles in medicine and research; botulinum toxin is used therapeutically, and many toxins provide insight into cellular processes. Regulatory frameworks govern handling, labeling, and safety testing to minimize accidental exposure and environmental release.