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Poison Ivy - Toxicodendron radicans
Family: Anacardiaceae (Cashew family)
Poison ivy grows as a vine or low shrub. About 85% of humans can
be
exquisitely sensitive to the oil, urushiol, contained in its leaves, stems,
and roots. [1]
Live poison ivy vines and shrubs photographed at McKee Marsh Forest
Preserve, DuPage County, Illinois. |
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"Leaves of three, let them be" |
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Much has been made of the
recently discovered fact that the (manmade) increase
of carbon dioxide in earth's atmosphere has caused
the poisonous triumvirate of poison ivy, oak and
sumac to grow larger, more dense and profuse,
and the oil, urushiol, produced by today's plants is
more virulent than plants of 20 or even 10 years
ago. Poison Ivy loves carbon dioxide.
Your best bet is to avoid the
plants in the first place. Learn to identify the
plants and stay away from areas where they may lurk.
If you think you've been exposed, immediately wash
the skin with rubbing alcohol and / or copious
amounts of clean water. Remove contaminated clothing
at first opportunity and wash same. Clothing with
the oil on it can contaminate furniture and will be
a source of reinfection if not washed promptly. Pets
that have been in touch with the plants can carry
the oil on their fur. Tools used to cut the plants
can have the oil on them, and can cause a reaction
even weeks later, the oil being very persistent.
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Poison Ivy Berries are shiny green at first, then become whitish
and hairy in late summer. These were photographed in late July.
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The most common ill effect suffered by humans is a
dermatitis caused by contact with oils in the plant's
foliage. Rashes and blisters erupt on the skin, sometimes
oozing and weeping, and always causing a extremely
irritating itch. Less common but more dangerous is contact
with smoke from burning ivy plants; the oil that causes the
allergic reaction can be carried on smoke particles and can
be deposited in the eyes, ears, or inhaled where it can
cause serious lung problems. A high percentage of forest
firefighters are stricken with ivy poisoning every year.
Common Myths about Poison Ivy
Myth: Scratching the itch will cause the rash to spread.
Fact: Once the urushiol oil has bonded to the skin (the
process taking only a few minutes), no amount of mechanical
action is going to move the reaction to other parts of the
body. Scratching does damage the skin but I can tell you
from bitter experience, it is nearly impossible to resist.
What is known: Washing the rash with very hot water can
release histamines in the skin that can bring dramatic
relief from itching, sometimes for hours. Care must be
taken, of course, not to burn yourself.
Myth: "I touch the plants all the time and never have a
reaction. I must be immune"
Fact: Studies show only 15% of humans are truly immune. The
other 85% will react with repeated exposure to enough of the
oil urushiol.
New leaflets are shiny and pointed
Myth: "I never touched a plant, but I got a rash. It must
travel through the air."
Fact: The oil urushiol does not become airborne except in
smoke and soot from burning poison ivy plants. However,
there are many other means whereby the oil can travel
invisibly: pets can pick up the oil on their fur and
transmit it when handled, touching wood upon which the
plants once grew can be a source of contamination, and
the oil can be deposited on clothing only to be transferred
to the skin on later contact. Repeat after me: Poison ivy
does not travel through the air.
Myth: "I get poison ivy when it rains."
Fact: The oil urushiol does not travel through rain. It can
be present, however, in lakes and river water near where the
plants grow, or where poison ivy or oak leaves, vines or
roots trail into the water. Urushiol can easily be retained
on rain gear exposed to the plants.
Myth: Drinking the milk of cows or goats fed on poison
ivy plants can grant immunity to the rash.
Fact: Studies show the milk of such animals contains no
urushiol and hence cannot desensitize us. Same is true of
honey made by bees from the flowering plants. (Pollen and
flowers of poison ivy do not contain the oil).
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Poison ivy and oak grows in
North America from Mexico to Nova Scotia, from
coast to coast except for areas of the desert
southwest. They prefer to grow at altitudes less
than 4,000 feet. They prefer full sun but will
grow in deep shade (as evidenced by the
accompanying pictures; they were taken in the
deep shade of an oak - hickory forest glade).
They favor dry soils but can tolerate moisture,
and they love disturbed soil.
Poison Ivy will grow in profusion on roadside
and railroad embankments, along forest trails,
in suburban backyards, and in city parks.
Myth: Eating poison ivy
leaves can make you immune.
Fact: Eating poison ivy is inviting reactions in
the mouth, throat and anus. 'Nuff said?
Myth: Washing with yellow or
brown laundry soap can prevent a reaction even
after exposure to the plants.
Fact: Soap has no effect on the oil urushiol.
Urushiol must be neutralized by a solvent such
as rubbing alcohol, or diluted with lots of
water. Soap won't hurt as long as it is used
with lots of water.
Myth: Washing with the juices
of the Jewelweed plant (Impatiens
capensis) can prevent or cure reactions.
Fact: Although this folk remedy has ample
anecdotal support, science has not been able to
replicate the effect in experiments.
Myth: Home remedies are
useless.
Fact: Although scientific proof of the efficacy
of a certain remedy may be lacking, they can
indeed bring dramatic relief to some
individuals. The mechanism of such relief is not
well understood, but may be comprised in part by
a powerful placebo effect. As long as the remedy
works and does not further damage the skin, it
is probably useful. |
Poison Ivy vines are covered with reddish
rootlets anchoring them to the tree's bark |
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Aerial rootlets are indicative of poison ivy, whether growing as a
vine or shrub |
Poison Ivy can grow as a climbing vine |
The vines can reach high into the forest canopy |
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Poison ivy leaflets can be quite large - up to about 6 inches long
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References
- Susan Carol Hauser,
A Field Guide to Poison Ivy, Poison Oak, and Poison
Sumac: Prevention and Remedies, Third. (Falcon,
2008).
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