An antitoxin is a substance that fights against a specific poison or toxin. Your immune system can create antitoxins to neutralize certain toxins, like a lock designed to fit only one key. Scientists can also make antitoxins outside the body and use them as medicine.

Doctors discovered antitoxins in the late 1800s when they realized that blood from animals who had survived certain diseases contained something that could help other animals with the same disease. This led to life-saving treatments: before antitoxins existed, diseases like diphtheria killed thousands of children every year. Scientists learned to inject horses with small amounts of toxins, wait for the horses to produce antitoxins, then extract those antitoxins to create medicine for humans.

Today, antitoxins remain crucial treatments for dangerous conditions. If someone gets bitten by a venomous snake, doctors administer an antitoxin (often called antivenom) specific to that snake's venom. The same principle applies to treating botulism, tetanus, and other toxin-based illnesses. Each antitoxin works against only one type of toxin, which is why doctors need to identify exactly what toxin they're treating before giving the right antitoxin.