Tim's Poison Ivy - July 2009 - Show Me a Memory
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Urushiol, the oil of all three plants, oil that causes the rash, is very potent: 
- Only 1 nanogram (billionth of a gram) needed to cause rash 
- Average is 100 nanograms for most people 
- 1/4 ounce of urushiol is all that is needed to cause a rash in every person on earth 
- 500 people could itch from the amount covering the head of a pin 
- Specimens of urushiol several centuries old have found to cause dermatitis in sensitive people. 
- 1 to 5 years is normal for urushiol oil to stay active on any surface including dead plants 
- Derived from urushi, Japanese name for lacquer: when the Japanese restored the gold leaf on the golden Temple in Kyoto, they painted the urushiol lacquer on it to preserve and maintain the gold. Guess you could say that you would be caught red handed if you stole it.

Source:  http://poisonivy.aesir.com