(CNN) Ricin is a natural, highly toxic compound that is a byproduct of processing castor beans.
If inhaled, injected or ingested, less than a pinpoint of ricin can kill a person within 36 to 48 hours due to the failure of the respiratory and circulatory systems.
There is no known antidote, according to the US Centers for Disease Control and Prevention. The most important factor, it says, is getting the ricin off or out of the body quickly and providing medical care to reduce effects of poisoning, such as assisting in breathing or flushing a person's stomach.
If ingested, ricin causes nausea, vomiting and internal bleeding of the stomach and intestines, followed by failure of the liver, spleen and kidneys, and finally death by collapse of the circulatory system.
One molecule of ricin will kill a cell it enters. Ricin ingestion is not always fatal; children are at more risk than adults. Ricin poisoning is not contagious and cannot spread from person to person through casual contact, the CDC said.
If a castor bean seed is swallowed whole without damage to the seed coat, it will probably pass harmlessly through the system. But if the coat is chewed or broken and then swallowed, the poison will enter the body.
The CDC says unintentional exposure to ricin is "highly unlikely," except through ingestion of castor beans. "It would take a deliberate act to make ricin and use it to poison people," it says.
If injected, ricin causes the immediate death of the muscles and lymph nodes near the site of the injection. Failure of major organs and death usually follows.