It is true that a few people are never allergic to poison ivy. But it is also true that some people don’t react to the poison ivy resin (called urushiol) at first, but become reactive later. Very possibly about 85% of people are allergic to urushiol –if not now, then at some point in their lives. The human body’s immune system response to urushiol is complex, and scientists are only beginning to understand it. If you are exposed to urushiol, you should wash it off your skin as soon as you can – within an hour if possible. Cold water works well, and also rubbing alcohol (and you can find some special products at the drug store if you want). What you want to do is keep the urushiol from sinking into the skin (since hot water opens your skin pores, stay with cool water). Once the urushiol sinks into the deeper layers of your skin, your body’s immune response will probably start fighting it. The redness and blistering of your skin are actually collateral damage inflicted by your immune system in the effort to destroy the urushiol.
How do you recognize which plants NOT to touch? Most poison ivy plants have leaves in groupings of three (though there are other, harmless plants that also have this pattern of three). Our local poison ivy is usually found as a vine (shown in the drawing in its winter/early spring state as a thick, hairy vine twisting around a tree trunk) or a low-growing plant. Sometimes the leaves have a nick in the sides, or several nicks, or none. Often the leaves are attached to stems that show a reddish tinge. Sometimes the leaves are shiny, sometimes they are matte. Poison ivy shows a lot of variety in its form. Poison oak leaves have the 3-grouping, with more rounded nicks in the leaf shape. Poison sumac deviates from the “group of 3” structure – it’s usually in bush form with leaves in groupings of 7 to 13.
So why doesn’t your dog get a rash? I can’t find the answer to that one. Humans seem to be the animal that is most reactive to urushiol. Deer actually enjoy eating poison ivy leaves, and are not harmed by it.
As people clear more land and build more roads, poison ivy growth increases because the plant prefers open but partially shaded areas. At the same time, as the deer population decreases near developed areas, the poison ivy is not getting eaten as fast. And then it turns out that climate change is a bonanza for poison ivy! As the level of carbon dioxide increases in the air, green plants grow faster, and the vine plants respond especially well. Poison ivy plants are much larger in our area than they were 50 years ago, and the urushiol they produce is significantly more toxic now.
At the Phinizy Swamp, science center staff put a concerted effort into keeping poison ivy off the paths and boardwalks. Poison ivy grows quickly, though, and you can often see it on the edges of the paths – because an open but somewhat shaded area is its ideal location. It’s a good idea to learn to recognize the plant.
For more information about visiting the Phinizy Swamp: