Poison ivy is a problem commonly encountered while caching. In most people, it causes a rash, however some people have little or no sensitivity to the irritant oil, which is called urushiol.
The plant is characterized by 3 notched leaves. The middle leaf looks like when you put your hands on top of one another, with the thumbs outward, and the outer leaves look like a mitten with a thumb. The plant is sometimes confused with Virginia Creeper, which looks similar to the poison ivy plant, only with 5 leaves. Both plants have hairy vines.
Some plants look similar (wild blackberry, for one) but are not poison ivy. As a rule of thumb: Leaves of three, leave it be.
The oil in poison ivy that causes the rash.
Urushiol can remain active for years, it is NOT inactivated during winter. Specimens of urushiol several centuries old have found to cause dermatitis in sensitive people. Urushiol may remain on clothing, shoes, gardening implements, or even your dog's fur for a long time. A good washing with an oil-cutting detergent should remove it. Wiping down with alcohol will cut the oil and wipe it away. Burning poison ivy releases urushiol into the smoke, which can cause a reaction on the skin or in the lungs or airway.
Urushiol is released from the plant when the plant is damaged, which happens when you brush up against it or step on it. Someone else or some animal could have damaged the plant long ago as well without your knowlege, so don't gently handle the plant and assume that you will not have a reaction.
Some people may be immune to the urushiol, but it is a sensitizer, so most people will eventually become allergic after repeated contact.
Once a person comes into contact with Urushiol, a rash may form within hours. It is important to wash the affected area as quickly as possible with a detergent. It would also be a good idea to wash all the clothes that you may have been wearing when you came into contact with the plant. Reactions can last from days to weeks.
It is important to remove the oil from the skin as soon as possible after contact occurs. Wiping down the skin with a soft cloth dampened with rubbing alcohol can halt the reaction. BigWhiteTruck, who is very sensitive to poison ivy always does this at the first sign of a rash forming, and swears that it keeps the rash from getting worse.
It is not true that poison ivy can "get into your system", and spread throughout your body. What is actually happening is you have multiple exposure sites that are appearing at different rates, or there is still urushiol on your body or clothing that you are unknowingly spreading yourself. That is why it is important to wipe down the skin and wash the clothing that may have come into contact with the plant as soon as possible. Also, wounds and blisters that may occur during the rash do not carry urushiol, so people can't get it from coming in contact with the affected skin.
In some cases, medical professionals such as your family doctor will prescribe heavy-duty anti-inflammatory drugs such as prednisone which will reduce the reaction.