OUT FOR POISON IVY
May 16, 2010
Q: I think
I have come in contact with poison ivy or maybe poison oak. How can I
find out what these plants look like? How much of a problem are they?
Do you have to touch the leaves to get the blisters on your skin?
is the most likely time for people to encounter an age-old outdoor pest
of the plant variety-poison ivy. And poison oak. Most botanical field
guides distinguish between poison ivy and poison oak. But the differences
are subtle and do not really matter in identifying the plants. The two
most definitive traits are the presence of three leaves on each stem and
a red coloration at the apex where the three leaves connect. Both plants
produce the oils that make you itch. Some biologists claim that poison
oak is more virulent than poison ivy. I do not think that has been firmly
documented. And I suspect someone who is itching like crazy from exposure
to either plant doesn't care which one is more virulent.
can climb trees as a vine (usually attaching close to the trunk), look
like a shrub, or be a single, simple plant. All parts of a poison ivy
plant--leaves, stem, fruits, and roots--produce oils that can cause skin
irritation in some people. Any bodily contact 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 also
get poison ivy in the winter simply by touching the stem, even though
the leaves are gone.
I work at
an ecology lab with people who spend time in swamps, woods, and streams
where poison ivy is as common as a household word. Yet few of us ever
get a serious case. Perhaps ecologists and others who are in the woods
a lot avoid the plant without being aware they are doing so. Also, most
people have no reaction when they casually brush against poison ivy, and
a third or more are not sensitive at all.
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. You cannot give poison
ivy to others, except by bringing them into contact with the oils that
are on your own body or your clothes after encountering the plant.
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 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.
to my favorite dermatologist, the symptoms of poison ivy are a consequence
of the oils causing a contact dermatitis (inflammation of the skin). But
she says that superficially similar dermatitis can be caused by numerous
other plants and even commercial products we might come in contact with.
Among the plants known to cause dermatitis are black walnut trees, red
cedar, and fresh okra. Fortunately, most people are not affected by those
and other information about poison ivy go to www.srel.edu/outreach/outreach.html.
Click on Educational Materials, then on Ecology Fact Sheets. Under General
Ecology, click on Poison Ivy. And when you are out in the woods this spring
and summer, remember to watch out for three leaves with a touch of red.
you have an environmental question or comment, email