I got a request for information about poison ivy and decided to repost an article that I initially published a couple of years ago.
Links have been updated accordingly.

Dr. Ramona Bates put up a post on her Suture For A Living blog about poison ivy. I was planning on doing the same thing, but she beat me to the punch. Her post did more than scratch the surface, but since we’re just starting to see poison ivy creep into the ED lately (ooh I’m on a roll), I wanted to add a few things.

Blistering or a rash that is in a line suggests some sort of contact dermatitis – usually from a plant or something stationary. Imagine walking past a plant and the edge of the leaf dragging against your skin. If you look at the picture on Dr. Bates’ site, the man’s arm has blistering in a line that is typical of poison ivy exposure. Another example is here.

While touching someone else’s rash generally won’t give you a rash (poison ivy isn’t “contagious”) sometimes you can get secondary contamination from things that have come into contact with the poison ivy plants. If you were walking in patches of poison ivy, it is possible to transfer the plant resin to your hands when you take off your shoes. If you pet your dog after your dog walked through poison ivy, you can transfer the resin from the dog’s fur to your hands. Then if you itch your face with your contaminated hand, you may develop a rash on your face.

The chemical that causes the reaction, urushiol, isn’t easy to wash off. If you get to it in the first hour or so after exposure, soap and water may remove it. After that, it penetrates into your skin and binds to the proteins in your skin so that ordinary soap and water will have little effect in removing it.

Once you get the rash from poison ivy and start itching, treatment involves getting the chemical off your skin and relieving the symptoms.
Tecnu and Zanfel are commercial products that wash away the chemical urushiol from the skin. If you use them early enough, you can significantly lessen your symptoms, although they reportedly have some effect for several days after exposure. Store brand products may work just as well and are considerably less expensive. Interesting point from another site is that Tecnu was initially developed to remove radioactive fallout dust from the skin and is a distillate of gasoline. This site also states that other organic solvents such as rubbing alcohol may work as well as Tecnu for removing urushiol – when rinsed with copious amounts of water.
Ivy Block blocks the urushiol from coming into contact with the skin and actually absorbs some of the urushiol. Lather up before you go out into the bushes and you may save yourself from even getting the rash. Just remember to rinse the Ivy Block off and reapply if you’re out for more than 4 hours.
One trick I learned for any kind of a bad itch is to use an ice cube to do the itching. The ice won’t scratch (and therefore irritate) your skin and the cold will help to get rid of the itch. When you’re done, you just throw out what’s left of the cube. Repeat as often as you want.
Domeboro solution (or Burow’s Solution) will help take away the itch. Mixing the packet with a small amount of warm water to dissolve it and then adding cold water to reach the proper dilution will create a cool compress that will help relieve the itching even more.
Use of steroids to treat poison ivy rash of poison ivy is debated. Some people swear by them, some people swear at them. I’m in the latter category. I generally don’t prescribe steroids due to the incidence of “rebound” symptoms if they are discontinued early. In this case, “early” is considered less than 2 weeks. That’s right – the books recommend that someone be on steroids for two weeks if the steroids are used to treat poison ivy. Sometimes you need steroids if the symptoms are severe or involve the eyes. On the other hand, I have seen multiple cases of rebound symptoms when a patient’s primary care physician gives a patient a Medrol DosePak for mild symptoms, the patient runs out over the weekend, and then the patient comes to the ED worse than when they started.

If you still have questions, this is a fairly comprehensive article on poison ivy for non-medical types and here is an article from eMedicine for the more medically-inclined.

Remember: Leaflets three -> let it be. Berries white -> poisonous sight. [Picture credits here]

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