From a thread on poison oak at High Sierra Topix:
Before I moved to South Lake Tahoe I lived in Santa Cruz. This was in the late-90s. The house I stayed in was located in a wooded area called Pogonip. One of my housemates had a dog. One day in springtime I was playing with the dog. I came up behind him and straddled him like a horse. I leaned over and petted him on his head. I was wearing shorts.
36 hours later I was at work. I started feeling tingly on my legs. I kept joking to my coworkers that I was having an allergic reaction to my laundry detergent. That evening, I removed my clothes to discover strange red marks all over my legs, hands and arms. The next morning the rash started. It spread all over my thighs, calves, wrists, arms, nose, ears and neck. Some of you might not believe this but the rash lasted for over six weeks. It just wouldn’t go away! It was hot and humid that spring in Santa Cruz. It seemed the humidity made it worse. It was so bad on my inner thighs I could barely walk. Just the vibration of taking steps was excruciating.
Poison oak is the bane of Bay Area hikers — I’ve heard horror stories of people ending up in the emergency room from severe allergic reactions. If you click on the link above and scroll down a ways you’ll find a high-res picture of poison oak; it’s nice to know what it looks like, though knowing what the leaves look like isn’t much help in the winter, when the leaves fall off and the plant stems still carry the resin that causes the rashes.
Here’s a list of poison oak tips (the tips are for trail builders but they appear to be good general advice.)
I don’t know if this is a myth or not, and there is NO WAY on earth that I’m going to test it, but…
It is said that you can develop an immunity to the oil by chewing on the leaves of the plant in the spring when the leaves are new. They say that the young leaves don’t contain enough oil to cause a big reaction.
If you try this and don’t die, I would be interested to hear if it worked.
Here’s another page of poison oak info:
http://www.knoledge.org/oak/
The author of this page says poison oak sensitivity increases with mulitple exposures, so even if you start out feeling like you’re immune, you’re apt to get it worse over time.
He pretty much discounts the notion of ingesting or smoking the leaves of poison oak.
I’m a chemist and not a doctor – don’t diagnose yourself based on my advice go see a real doctor. Always carry Benadryl or similar antihistamine in your backcountry first aid kit, just in case someone does have a severe reaction.
—
Here’s my understanding of why purposefully exposing yourself to poison oak/ivy is a bad idea:
The body’s reaction to poison oak is what’s called a Type I allergy. Type I reactions are when the body is hypersensitized to a protein in something by its own IgE antibodies – detailed info in: Wikipedia’s allergies article
Because the reaction is an immune response and those don’t “go away” after a few years, each time you are exposed to poison oak oils/proteins your body will produce additional antibodies that target it, causing a more severe reaction with each exposure.
Yes, there are other ways poison oak can cause reactions, but the reaction of IgE antibodies is the overwhelming way it invokes a response and the most common reason it can be life threatening in the backcountry.
I make a great poison oak/ivy soap and cream…have been a outdoor enthusiast for 30 years…and married a terribly allergic man…developed this over the last 20 years. Welts of poison oak reaction disappear within an hour of applying soap and cream together…mugwort, homeopathy and clay are the basics…Mugwort is a poison oak sufferers best friend…rubbing on your clothes and dog works as well as your skin…Tecnu is paint thinner…not great for the body or mind, there are effective alternatives.