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Poison Ivy. Photo: <a href="http://upload.wikimedia.org/wikipedia/commons/4/4f/Poison_Ivy_in_Perrot_State_Park.jpg">SWMNPoliSciProject</a>, Creative Commons, some rights reserved
Poison Ivy. Photo: SWMNPoliSciProject, Creative Commons, some rights reserved

Poison ivy: neither poisonous nor ivy

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But you should still definitely avoid the stuff.

"Leaves of three, let it be." Martha Foley and Dr. Curt Stager talk about one of the common and annoying menaces to enjoyment of the outdoors.

They discuss whether it's really an ivy, why we call it "poison," and how humans and animals react differently to the plant.

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Martha: Let’s talk about poison ivy. First of all, you say it’s not an ivy. I can see that, it doesn’t look like ivy to me. Why do we call it poison ivy?

Curt: It dates back to the 1600s; an early naturalist thought it looked like British ivy.

MF: So we still call it ivy?

CS: We still call it that. And it made people itch back then so he called it “poison” ivy.

MF: So here we are; poison ivy. Most people who go for a walk in the woods are taught early in their lives what to look for. Can you give us a quick sketch?

CS: “Leaves of three, let it be.” is the catchphrase. It’s got basically a little branchy point with three leaves on it. It can be growing up trees sometimes, it’s a groundcover thing. When the little berries are mature they are white.

MF: Leaves are shiny?

CS: Leaves can be shiny. Even without the leaves, the vines will also have the oil, or resin in them. Pretty much any part of the plant has an effect.

MF: So once those three leaves are gone you are pretty much on your own for spotting poison ivy vines. Is it a poison?

CS: Well, that’s a funny thing too because you think if it’s a poison, like cyanide or something, it would kill everything. But it turns out a lot of animals eat it with no ill effect. Livestock will eat the leaves, birds will eat the berries. It’s mostly humans that react. So it’s not exactly a poison in that sense. It is more like an allergy than anything else.

MF: It seems like everybody gets poison ivy at some point.

CS: You’d think so, but then if you really ask people, it turns out that only about half of us would get that reaction if we brushed up against a leaf. If you went to a mad scientist’s lab and they took some of the resin out and spread it on you, about three-quarters of us would react to it. So it’s really not everybody, which again suggests that it’s not a real poison as much as an irritant. In fact, the technical term for it is “contact dermatitis.” This is where your skin gets inflamed on contact with it.

MF: So all the times I told my mother, “I never touched it, I never touched it.” I must have just walked near it? I was actually not being quite accurate. You have to have contact with this resin?

CS: Right. But you might not always know you did have contact with it because the stuff can actually stick on your clothes or tools, or a pet. If it gets on you then, you might not notice it right away because different parts of your skin react differently. So it could actually be days or even weeks later after your exposure that you get the stuff.

MF: Now I know you’re supposed to wash it off if you know you’ve touched poison ivy or poison ivy’s on your clothes or anything. You wash and you wash your clothes. So this reaction could happen a week later even after you’ve washed this stuff off? It is just the skin taking a long time to react?

CS: Right. I remember a long time ago, when I was little, getting it. I was in Connecticut and I’d get it all the time. People would say, “Oh, don’t scratch it you’re going to spread it.” Well, maybe just after you’ve gotten the resin on you it might spread.

MF: If it was still on you?

CS: If it was still on you, you it might spread it. But actually later on, the reason it can seem like it is spreading is because it is just the different parts of your skin reacting at different rates. Other parts are just playing catch up, but had already been exposed.

MF: Do get more sensitive or less sensitive? If you’ve had poison ivy would you be more sensitive to it the next time?

CS: Well, there actually is a trend with age. You are most susceptible your first thirty years of life and then it drops off through time. There are actually other plants besides poison ivy that have the same chemical in them. In fact, a lot of plants in the same family, the cashew family, have this. There is a tree in Japan called the lacquer tree that has this. It is used for traditional lacquering of bowls and plates and stuff like that.

MF: Yes, lacquer.

CS: So the workers there have to become used to the stuff they are working with because they get this kind of a poison ivy reaction from the lacquer they’re using in the traditional arts. It takes them awhile, but they can actually build up a resistance over time.

MF: Ewww, those first few years must be just killer.

CS: Well, the most amazing thing is the lacquer itself on those objects can set off some people’s reaction too. Even centuries later on the old artifacts, they touch it and some people will get a poison ivy reaction from that.

MF: That’s not fair. That’s just not fair.

CS: There’s a new chapter on this poison ivy story now which is just another reason to be concerned about global warming. Some scientists down at Duke University took poison ivy plants and they put them in these chambers where they could control the atmosphere it was growing in. They put some in air that was like the 1700s and they put some in with air that is more like now, with more carbon dioxide from fossil fuels in it. And they put some in like it’s supposed to be in the next century.

MF: More carbon dioxide?

CS: Yep, more carbon dioxide. And low and behold, poison ivy loves carbon dioxide.

MF: So it’s going to be like kudzu?

CS: It grows faster, it grows bigger, it makes more of the irritating resin, and the irritating resin is more irritating.

MF: All good, it’s all good.

CS: You’re going to need an ocean of calamine lotion.

MF: …in the next century.

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