Ricin is in the news this week because the Secret Service says that a letter containing the substance and addressed to President Obama was received on Tuesday at a White House mail facility. Two more letters sent to Sen. Wicker and Senator Joe Manchin (D.-W.V.), has been found to contain ricin.

Ricin is a lethal protein taken from the castor bean and used as a biochemical testing agentand causes deadly swelling and bleeding if taken internally.

Ricin can be made in a powder form, mist, or pill, it can also be mixed in water or mellow acid. People can inhale ricin powder and be contaminated. It would take a deliberate act to make ricin and use it to poison people. Accidental exposure to ricin is highly unlikely.

Ricin has no known antidote and can kill, if inhaled, within 36 hours. Merely touching it, though, is not fatal, but may cause a rash.