Poison ivy can be a found as
creeper,
climber, or a
bush. Published records of poison ivy in
North America date back to the 1600s when Captain
John Smith coined the term 'poison ivy' in 1609. It was introduced to England in 1640.
There are actually two varieties of poison ivy: climbing variety (toxicodendron radicans) which is also known as poison oak in its bushy growths and the non-climbing variety (toxidendron rydbergii) which is also known as Rydberg's poison ivy. However, both species interbreed, look very similar, have the same preferences, and give the same rash thus the differences between them is purely academic. The taxidermic classification is
The irritating factor is that of Urushiol Oil, which comes from the
Japanese word urushi meaning lacquer. The origins of this come
from the restoration of the gold leaf on the Golden Temple in Kyoto,
Japan.
It was painted with urushiol lacquer to preserve and maintain the gold
and any potential thieves would have a bad case of itching.
Urushiol oil is also a very potent irritant that only requires 1 nanogram (one billionth of a gram) to cause a rash. 0.25 ounces of urushiol oil would give a rash to every person on earth, and 500 people could would itch from the amount on the head of a pin. The oil can stay active for up to five years on any surface, and samples from centuries old sources have caused itching on sensitive individuals.
The oil is part of the sap of poison ivy and appears on all the surfaces of the plants, including that of the roots and berries. Damaging the leaves or berries will release more sap and thus poison ivy rashes are especially common in the spring when leaves are tender.
If you come in contact with poison ivy it is possible to get the oil off of the skin. Aside from numerous products the appropriate procedure is to wash the area with cold water. Hot water will open the pores and allow the oil to move further into the skin. This has the best chance of working within the first hour after contact, though the oil may bond with the skin in less than 15 minutes and water will become less effective. Furthermore, cold water helps to inactivate urushiol. Avoid using a washcloth. Rubbing alcohol is more effective than water and may work within the first 4 hours. The key point in this is to use as much water as possible - using only a small amount will just move the oil around, spreading it rather than removing it.
If the oil is already established and a rash is forming that itches one of the best approaches is to speed it up. By immersing the rash in the hottest water that can be taken the release of histamines (which cause the itching) is drastically accelerated. As these chemicals are used up (and only slowly replaced) it can provide several hours of relief from itching. During the period of heating, the itching will actually become worse as the histamines are released. This does not reduce the duration of the rash, but rather alters the severity of the itching.
see poison ivy rash treatment for more specific information on the treatment of the rash from poison ivy.
For more information (and a significant source for the above information):
http://poisonivy.aesir.com/