by Whit Gibbons

April 25, 2004

According to the National Park Service, spring is the most likely time for people to succumb to an age-old ailment of being outdoors-poison ivy. But ecologists, hunters, and wildlife managers who spend time year-round in swamps and woods where poison ivy is a common plant, seldom get a serious case of poison ivy. Maybe they are unconsciously cautious and actually avoid the plant without being aware of doing so. Also, most people have no reaction when they casually brush against poison ivy, and 20 to 40 percent are not sensitive at all. Some people spend their lives around poison ivy without ever having a reaction.

Poison ivy is an eastern U.S. plant with three leaflets at the end of each stem. The stem holding the leaflets is usually reddish, and all parts of the plant--leaves, stem, fruits, and roots--produce an oil that can cause skin irritation in some people. Any contact of the body with the oils can cause a problem, whether from patting a dog that has just walked through poison ivy or touching clothes that have come in contact with the plant. You can even get a case of poison ivy internally by inhaling oil droplets that become airborne in smoke when the plants are burned. You can even get poison ivy in the winter simply by touching the stem, even though the leaves are gone.

The facts, myths, and disagreements about the properties of poison ivy are legion. You do not spread poison ivy by scratching where it itches, despite what some people say. New blisters and irritated areas can appear more than a week after exposure to the oils, but these merely represent the normal lag time that can occur after initial contact. Also, you cannot give poison ivy to others, except by bringing them into contact with the oils that are on your own body or clothes after encountering the plant.

Many forms of wildlife can eat poison ivy without being adversely affected. Dozens of kinds of birds including bobwhite quail eat the fruits, which are clusters of smooth, white berries that appear in late summer. I know of a serious case of poison ivy being contracted by a wildlife student who sorted through the stomach contents of a recently killed deer. Among the data he recorded for his research on the diet of deer was that they sometimes eat a lot of poison ivy leaves.

I checked with my favorite dermatologist to find out something about the symptoms of poison ivy. According to her, the oils cause a contact dermatitis (which means inflammation of the skin) that cannot be distinguished from one caused by numerous other plants and products we might come in contact with. Among the plants known to cause dermatitis that is superficially similar to that caused by poison ivy are black walnut trees, red cedar, and fresh okra. However, many, possibly most, people are not affected by contact with those plants.

The skin irritation--blisters, burning, itching--normally occurs 24 to 48 hours after contact with any part of a poison ivy plant, and expression of the ailment follows a bell-shaped curve. The most severe symptoms occur midway between a 2- to 24-day period. One treatment for relief of the symptoms of a severe case is a steroid, such as prednisone. The steroid masks the symptoms even though the body's response to the irritation continues. My dermatologist cautions that some doctors treat with steroids for too short a period. Thus if your reaction is following a 24-day cycle and you take steroids for only 7 days, the symptoms could reappear before the peak of irritation has been reached.

Most botanical field guides distinguish between poison ivy and poison oak. Subtle differences are noted, ones that do not really matter for recognizing the plants. Both have three leaves and produce the oils that make you itch. Some biologists claim that poison oak is more virulent than poison ivy. I'm not sure about that part, but I do suspect that under certain circumstances any of us can succumb to these three-leaved plants, so watch what you touch when you are in the woods this spring.

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