What Poison Ivy Has Been Up To While You Weren't Paying Attention


So I'm currently working on an article for Prevention magazine about some of the surprising ways that climate change can screw with your health. The thing I least expected is the dirty lambada of destruction being danced, as we speak, by global warming and the common North American Toxicodendron radicans.

Part of what makes this so nifty to me, is that, once you think about it, it's sort of a "duh" moment. While not so great for you and I, carbon dioxide is, basically, plant food. I'm told that rising levels of CO2 in the atmosphere affect different plants in different ways, but poison ivy is definitely one of the winners of global warming. For this unpleasant little weed, more CO2 seems to mean more growth

But wait, it gets worse. Lewis Ziska, a plant physiologist with the Agriculture Research Service of the U.S. Department of Agriculture, has been studying poison ivy both in the lab and out in the natural wilds of Duke University's research forests. He says that, not only is poison ivy growing fat and happy on the spoils of our carbon emissions, but that plants getting more CO2 also produce more, and stronger, levels of urushiol---the toxin that makes the ivy so darned appealing to begin with.

In fact, while other factors like the local growing season and the amount of light the plants are getting can alter CO2's results, Ziska says we can definitely see a difference between the poison ivy of today and the stuff your parents were chasing each other around with at Camp Thankgodthekidsrouttastate 50 years ago.

Um...happy summer!

Photo courtesy quinn.anya


  1. Finally! Global warming will hit home for the little spawns of those who deny global warming. With one hug or one load of laundry the entire fam will be happily scratching their skin off until the end of time with ALL NEW MUTANT POISON IVY!

  2. Is poison ivy especially good at absorbing CO2? I wonder if it would be possible to farm poison ivy in a controlled environment with the goal of reducing CO2 in the atmosphere.

  3. It’s been pointed out that under capitalism’s ideology the Amazon rainforest has no economic value until it’s been cut down (for the wood, land space, etc.). Noting recently how a guy paralyzed for 20 years regained use of his legs after a spider bite, I wonder if there isn’t some way to make a product with economic value from the poison in pests like this. Then you can offer a “bounty” per harvested and bundled kilo and let market forces take its course. They do a similar thing in Oz for kangaroos. Pet food and and ornamental skins with a base government bounty per carcass… Employs a decent number of people with high powered rifles full time.

  4. @2

    I’d doubt farming it would be a good idea. I have a fair amount around our home (in the city none the less) and from everything I’ve read harsh sprays and manual removal are the only ways of getting rid of it.

    Burning it releases the urushiol into the air which can cause burning and scaring of the lungs if inhaled. Composting it also causes other issues if it is used to quickly. I can’t see anyone wanting to deal with acres of this stuff once it has grown to full size…

    Reminds me of kuduz, which in the south we have plenty of (and I have that growing around my house as well…) Oh and I’ll throw English Ivy in that mix as well. Evil plants all of them.

    This also explains why playing in the stuff 20 years ago didn’t do anything to me and now I seem to more reactive to it. (Not to mention repeated exposure increases your sensitivity to it.) At least on me it’s tolerable. On my wife it looks like 3rd degree burns.

  5. Ooft! Is poison Ivy that bad? I’ve never experienced it…is it only native to North America?

    I suppose I should just look it up…

  6. This is all well and good, but the real question is whether she will be in the new Batman movie.

  7. Poison oak is absolutely THAT bad…and then some, especially if you get it on your face, or “down there”. This is one plant, that I personally have developed a severe antipathy for…I fear and loathe it! If you have never experienced it, consider yourself fortunate…

  8. Off topic, but that sign reminded me of ones in the Iguazu national park in Argentina – they simply said “Stay on the trail” in a couple of languages, and had a picture of a snake.

    I suspect that they didn’t say anything about snakes explicitly, because that would have been lying – but the signs sure worked better with a snake drawing on them…

  9. There wasn’t a year that went by as a kid in Massachusetts in which that shiny three-leaf bastard of a vine didn’t get all over me. You’d have the best day in the woods and then a couple of days later in school the pits between your fingers would suddenly scream out, “Surprise! Remember me? Good luck holding that pencil for the next two weeks!”

    Nice to know increased CO2 is upping the poison ivy challenge for the younger generations.

  10. Incidentally, just for the record, the last time I had a bad case of poison ivy I tried this stuff called Zanfel, and it worked almost instantly, getting rid of it.

    On the other hand, I recommended it to a friend who had it a few years later, and she found it completely ineffective.

    Still, if you’re stuck with other ineffective poison ivy “remedies” (shot of cortisone, Calamine lotion, etc), it’s probably worth hunting the stuff down and giving it a try.

  11. Geology tells us that high CO2 levels historically tie in with periods of REDUCED global temperature.

    The planet was hotter in the bronze age (virtually no man made CO2) than it is now.

    Why then, do people keep going on about CO2 and global warming in the same breath?

    Also, as best we can tell, every planet in our solar system is currently going through a hot spell – since we’re not running 4X4s on any other planet, but we all share the same sun, you have to wonder about the actual cause of our current climate change.

    I’ll don a flame proof jacket; I know that reasoned objective, scientific thought has no place in environmental discussions. Sorry.


      Because, of course, anyone who disagrees with you is by definition, unreasonable, subjective and unscientific. Thanks. Now I have an irony headache.

  12. No idea if this is useful to your article: there are people, my daughter and myself included, who are not allergic to poison ivy. We simply also do not react, or at least, not to the scrawny old version.
    Nice post, btw.

  13. @Will Tingle (#14): Do you have a citation for that?

    Honestly, I would be very very happy if you were right and all of this was just natural, but all things being even — ignoring that there is overwhelming evidence in the other direction that says we’re fucked — why risk being wrong?

    Moving away from coal and oil as energy sources are things we should be doing anyway, regardless of the potential looming threat of global warming (or “climate change”). If your argument is purely economic (and that’s the only one people seem to make about climate change), keep in mind that all of the energy available on earth came from the sun at one point anyway. With coal and oil, we’re burning hundreds of millions of years’ stash in a couple hundred because we can’t be bothered to capture use the energy the sun gives us for free every year in an efficient way. Inevitably we’re going to run out of the stuff and then we’ll really be fucked. Why not wean ourselves off of it now while there is still some left to do the weaning with? If global warming is a lie, I will be VERY happy. But why risk it?

  14. Don’t worry, the fact that kids never go outside anymore makes this non-threat! There is, I believe, little chance your Wii avatar will be exposed to the tri-foil terror. ;)

  15. I live in Georgia. I don’t remember poison ivy growing all over the place in the past but it seems to now…it’s all over my neighborhood. Also, I used to be impervious to its poison but now get horrible rashes. I guess this is good news for Roundup plant killer.

  16. Will Tingle, have you even taken a 100-level geology, astronomy, or earth sciences course?

    In the 100,000-year Milankovitch cycle, various factor align to either significantly raise or decrease the world’s average temperature. They then set off multiple positive feedback loops and either increase the amount of carbon dioxide in the atmosphere, raising the temperature and further increasing the amount of carbon dioxide in the atmosphere, or raising the albedo, and further decreasing the temperature and the amount of light absorbed by the earth’s surface.

    I’m surprised that you’ve taken such an odd stance, as most climate change deniers accept the fact that carbon dioxide is related to increased temperature, but claim that increased CO2 is merely caused by a natural rise in temperature, and not caused by humans. (Although C02 both causes and is caused by temperature increase- a positive feedback loop whose nature is often seen elsewhere in natural phenomena)

    From ice core samples we have a pretty detailed and accurate account of the history of earth’s temperatures (by comparing the proportions of two isotopes of oxygen). If you look at where we are in the Milankovitch cycle, it looks like we’ve been long due for a cooling trend. Of course, we shouldn’t worry about being “behind” on the cycle, but we should not think that this warming trend is linked to any forces outside of earth.

  17. I’ve fought many battles with poison ivy, won some…lost others badly. I’ve tried everything from ripping it out to covering it with plastic for 2 years. Salt. Vinegar. Bulldozing it and burying it under 6 feet of compost seems to work pretty well. I’m normally very averse to any kind of herbicide, but I have no problem taking out p.i. with some herbicide with a short break-down time that’s judiciously applied (rather than broadcast sprayed).

    What I’ve also noticed about the stuff is that it tends to be a border plant – it doesn’t grow in the middle of open fields OR deep woods. Near roads, between houses, small woodland areas, etc. That seems to be its habitat. So as we’ve create more roads and more houses (edge habitat) we’ve created more places for it to grow.

  18. I always thought that carbon dioxide had little effect on plant growth, because the limiting reagents were things like nitrogen and phosphorus. At least, that’s what I recall in response to claims that global warming would promote agriculture. Is this simply not true, or is there a reason Toxicodendron would be particularly sensitive?

  19. Poison ivy is the mosquito of the plant world. It has to serve some purpose, but there are many things that could fill its niche that are less annoying. BTW, one thing that helps reduce the itching and speeds healing is the topically applied sap of the jewelweed plant. A nice benefit is that jewelweed (or touch-me-not, as anyone who has played with the exploding seed capsules knows it) usually grows in fairly close proximity to poison ivy. Thank you, Euell Gibbons!

  20. As much as I love Euell Gibbons, jewelweed actually has quite a different habitat than poison ivy…it needs wet roots and tends towards the shady areas, poison ivy does not.

    (random fact about jewelweed: you can eat the seeds that bust out of the capsules. They taste like walnuts and are robin’s egg blue.)

  21. Zanfels works really well for me. It sometimes takes more than 1 treatment to be effective (probably depending on the degree of exposure.

    Everything you want to know about the Toxicodendrons:


    poison oak =Toxicodendron diversilobum, mostly in the Western US

    poison ivy = Toxicodendron radicans, mostly in Eastern US

    Poison oak and poison ivy account for an estimated ten percent of lost work time in the U. S. Forest Service. In fact, hundreds of fire fighters who battle summer and fall blazes in California’s coastal ranges are so severely affected that they are unable to work. People who breathe in the smoke and soot may develop serious inflammation of respiratory mucous membranes. Because of the serious economic impact due to lost employment time, poison oak “injuries” are covered by Workers’ Compensation Insurance in California. The monetary cost of this affliction is approximately one percent of the state’s workers’ compensation budget (Epstein, 1994).

    1. Does this mean other plants are becoming more plentiful and potent as well?

      If the temperature rises, borderline hot species will do better and borderline cold species will do worse, and vice versa with dropping temperatures. Depending on the composition of the local flora, a small number of species could displace a great deal of diversity. With rapid climate change, new-climate-tolerant fauna can’t move into the affected area as fast as the old fauna loses it’s climatic foothold, thus a net loss of diversity. It’s the rapidity that’s the problem, not the climate change.

  22. Years ago I noticed the increasing prevalence of poison ivy. Several naturalists and botanists told me it was my imagination. Then I started reading articles like this. Who’s laughing now? Well, not me, it really isn’t funny.

    Re: Hidflect, not quite commercialization, but decades ago the Army labs in Natick Massachusetts were working on weaponizing poison ivy.

  23. a-yup. Coral bleaching sounds like the end of the world – but it also means the northern limit of coral is expanding.

    I hear our pets will be the first victims of the wave of advancing diseases.

  24. #29

    Some plants. Not all. Frustratingly, it seems like this is largely a good thing for the most obnoxious members of the plant kingdom. Ragweed is getting a nice growth and pollination boost as well.

    Along the same lines…


    This variation between the effect on plants is probably why you’ve read that food crops aren’t growing more from CO2. Some plants like it a lot. Some don’t get the same benefits. I’m not sure that we know exactly why at this point. But I do know that Lewis Ziska is getting ready to start on some research into the genetics of this, with the eventual hope of transferring that beneficial effect to food crops.

  25. #7

    Poison ivy is proof that God exists. Nothing that evil could arise in a cold, mechanistic universe.

  26. “A toxic jungle now spreads, threatening the survival of the last of the human race.” – NausicaÃ¤ of the Valley of the Wind

    Fits in with the storyline, no?

  27. In Soviet Russia people eat poison ivy.

    … No this wasn’t a Yakov Smirnoff joke, I literally ate poison ivy.

    Turns out that if you boil it the itchy crap in it becomes harmless and the whole plant turns in to a sort of spinachy and somewhat tasty soup.

  28. I am ridiculously susceptible to poison ivy. I spend all summer with PI rashes on the backs of my legs from my dogs rubbing against me — contact PI! Ortho makes a brushy weed killer that is awesome on poison ivy. I spray it every year. I also walk around with poison ivy wipes when I go for a walk in the woods or on the beach. Three years ago I cut a one inch vine (in winter – no leaves) and got PI so severely I ended up in the hospital. Good times!

  29. Screw calamine! I go straight for the bleach. My grandmother swears by it, and I swear by my grandmother. It seems to dry out the blisters quickly, which keeps it from spreading. I f*ing hate PI!!!

    1. Oh boy, I had an unintended run in with tons of PI this evening on a bike ride. I came home and promptly scrubbed myself with soap and then doused my legs from the thighs on down with BLEACH. Hopefully this will do the trick, I haven’t had a run in with this sucker for over 20 years.

  30. #26: Many years ago I was seriously injured when I came too close to a pile of burning leaves and brush which, unfortunately, contained some poison ivy vines. My eyes were swollen shut, my face was covered with blisters and I was given injections at the local hospital as the MD’s were concerned about my breathing. This stuff is not just a pest plant- under the right conditions, it can kill you.

  31. For almost 40 years, I’ve eaten a little RAW poison ivy every spring and it gives me immunity for a season.

    When I was little I got PI severely. They gave me shots to protect me and I learned that the shots were just an extract. Then I learned in Brad Angiers “Back to the Woods” about eating a bit several times before it’s full-grown (and more potent).

    You want to pick a leaf by grabbing it with a non-PI leaf folded over. Toss in mouth and discard non-PI leaf. Chew and swallow, followed with at least a cup of water swirled around your mouth.

    ONE time I ate too much or too late in the spring, and got a bit coming out my butt. Still WAY preferable to when I used to get it over 70% of my body!

  32. Evanest has the right idea about eating a leaf of poison oak or ivy, but for someone really allergic, it could cause big problems, the least might be a rash on the roof of your mouth as one woman told me. The leaf has too much urushiol to be safe (I have eaten them too). I wrote a 40 page booklet on PI and PO in 1980, and am in the middle of a very serious book on the subject. It will be a year probably before publishing soft cover and e-book etc. I have come up with eating the skin of a mango. It cross sensitizes with the Toxicodendrons,because it is closely related to urushiol. Workers with all these plants, including cashew shell, japanese laccquer tree, painting lacquerware (urushiol tapped from the trees)all lose most of their sensitivity over time. But you need to continually expose yourself to the oils. I suggest drying mango skin on the window sill and eating a small piece, size of a nickel every day, or not more than 7 days apart. The immune system produces a blocking antibody that inhibits the immune reaction etc. But you have to continue introducing it forever. It may not work completly, but over time, it might at least cut down on the rashes. I went from head to toe to almost nothing, and I live in it.

  33. In over 50 years I had never gotten a Poison Ivy rash, and I’ve certainly been up close and personal with it. but this summer… I believe it got even with me because I was bragging about how I have avoided it and was not effected by it. It heard me… (soft voice says ‘open the pod bay door HAL’)

    Thus a visit to this very site, to see what gives and why now… interesting and enlightening conversations. Thank you all… now back to itching and scratching….

  34. Great poison ivy article.

    And to that guy who thinks that just cause he posts his environmental opinion, it must be scientific and true, (and thus justifies his Hummer)…..well boy, just cause you think something, it doesn’t make it true. And you may be VERY surprised one day. That’s all I can say, since I’m not arrogant enough to pretend that somehow I** get it better than leading specialists all over the world who are still working it out. And I’m sure glad your type of science isn’t the one favored by educated people. You say “I know that reasoned objective, scientific thought has no place in environmental discussions,” and I see you follow your own advice to the letter. No objectivity. No science.

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