What poisons can I safely take to build immunity to toxic substances? Does eating poison ivy build resistance to allergic reaction?

Dear Cecil: I’d like to become resistant to one or more toxic substances by gradually increasing my intake of them over time. Unfortunately, many poisons build up in the body, usually in fatty tissue, until the concentration is lethal. Cecil, which poisons can I safely take in increasing quantities to build a resistance? The Dread Pirate RobertsI’ve just been through my first-ever bout with poison ivy. Walking around with a bright red bumpy face has encouraged people to tell me of their remedies, but the strangest thing I heard was from two different people who told me that they’d eaten poison ivy to build up a resistance to it. Do people really do this? James Nelli, Columbus, Ohio

Cecil replies:

I’m seeing a problem right off the bat here, DPR, which is your use of the word “safely.” Deliberately exposing yourself to incrementally greater doses of poison (sometimes called mithridatization, after King Mithridates VI of Pontus, who reputedly pursued such a regimen) isn’t something that can really be done safely, any more than one can safely undertake to jump a nitro-burning funny car over a row of buses. Maybe you’ll make it, but the enterprise has a fair bit of risk built in.

To a limited extent, it is possible to build up a tolerance to certain poisonous metals. Metallothioneins are proteins produced in the body that, among other things, seem to bond to ions of dangerous elements like arsenic and cadmium and so help to minimize organ damage and other serious ill effects. While there’s no way to become immune to such poisons, chronic exposure to them may — I repeat, may — stimulate the body into upping its metallothionein output, thus allowing one to take on greater quantities of the toxic stuff before starting to get really sick.

Something along these lines might have been going on in the case of the famed arsenic eaters of Upper Styria, Austria. In the mid-1800s word got out to the wider world that a considerable percentage of Styrian peasants were ingesting potentially lethal quantities of arsenic (a by-product of the ore smelting going on thereabouts) on a regular basis, essentially as a health tonic — they believed it improved their breathing and complexion and helped them maintain a robust body weight. Many scientists scoffed, but academics familiar with the region vouched for the phenomenon. Fritz Pregl, a professor at the University of Graz, assured an American colleague in 1927 that arsenic eating was for real and remained common in Styria as of that time. The most popular delivery method, apparently, was to spread shavings of arsenic trioxide on a hunk of bread.

Some animal venoms may lend themselves to the mithridatic process as well. Several maverick herpetologists have reportedly developed partial immunity to various kinds of snakebite by injecting themselves with venom over a period of years; the most famous of these is Bill Haast, for decades the proprietor of the Florida tourist attraction called the Miami Serpentarium (he still runs a venom lab under the name) and the survivor of something like 170 poisonous bites.

There’s a degree of self-selection in effect here, though. The people who embark on a long-term program of venom exposure aren’t, I’m guessing, the kind of people who first write to someone like me to ask if it’s a good idea. If you don’t already have a garage full of deadly reptiles from which you extract venom regularly, my suspicion is you’re not destined to get involved in any kind of venom-shooting scene.

But if you’re determined to become resistant to something unpleasant, you could always start with poison ivy. The active ingredient in poison ivy (as well as in poison oak and sumac) is the chemical urushiol, a nasty and persistent oil contained in almost every part of the plant; contact with this stuff produces a serious allergic reaction in about 85 percent of the populace.

And as difficult as it may be to imagine doing, James, outdoors types have long advocated eating poison ivy leaves, in small amounts, as a way of building up one’s urushiol tolerance; Euell Gibbons recommends the practice in his foraging guide Stalking the Wild Asparagus. Does it work? Dermatological testing says yes — ingesting urushiol made subjects less likely to break out in a rash following skin contact. The benefits decrease fairly quickly over time, so you have to keep up with it, and one noted side effect is pruritus ani, also known as itchy ass syndrome. You can also develop urushiol resistance via injections, or through occupational exposure — the oil is a key ingredient in traditional Japanese lacquer.

Minimizing your reaction to poison ivy doesn’t have quite the same dramatic flair as rendering yourself immune to actual poison, true, but it may prove more useful. Increased levels of CO2 in the atmosphere, researchers say, may cause poison ivy to grow larger and more virulent in the near future — just another fun fringe benefit of global warming.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.