Poison Ivy, Oak and Sumac
by Nick Gromicko
In almost all suburban and rural regions of the United States and Canada, inspectors run the risk of developing potentially debilitating, allergic symptoms from exposure to urushiol-secreting plants. This potent, clear oil causes an itching rash (called contact dermatitis) in 350,000 people each year, but these numbers can be reduced through education and by taking appropriate precautions. Exposure can put sufferers out of work for days or weeks, and may even require hospitalization. Inspectors should learn to identify these plants -- especially the top three offenders: poison ivy, poison oak and poison sumac -- and protect themselves and their clients from the dangers lurking in yards across North America.
Urushiol oil is potent -- just 0.25 ounces of the allergen is sufficient to cause a rash on every person on earth, according to the Poison Ivy, Oak and Sumac Information Center. The oil begins to penetrate the skin within minutes after contact, but the rash usually takes 12 to 72 hours to appear, at which point the person experiences severe itching, redness and swelling, followed by blisters. While the rash appears to spread, it is not contagious, but it will continue to grow due to differing rates of the immune system's response to the oil.
A few other important facts about urushiol oil:
- A segment of the population – perhaps as much as 30% -- is not allergic to urushiol oil, although many people may become sensitized after repeated exposure.
- NEVER burn any plants described in this guide. Urishiol vapors can travel long distances, and inhaling them can create potentially life-threatening respiratory distress.
- Do not handle dead urushiol-secreting plants. The oil can remain active for several years, so handling dead leaves or vines can cause a reaction.
- Oil transferred from the plant to other objects (such as pet fur) can cause a rash if it comes into contact with human skin. Domesticated animals and wildlife do not appear to be allergic to urushiol.
- The oil may be removed with alcohol or cold water for a short period following exposure.
- Urushiol oil is found in virtually every part of the host plant, including the leaves, vines and roots. Tearing the plant in an attempt to kill it will release far more oil than can be contracted from just accidentally brushing against it.
The Three Most Notorious Allergenic Plants in North America
- Poison ivy accounts for the majority of contact dermatitis resulting from urushiol oil.
- Habitat: Poison ivy grows throughout much of suburban and rural North America, including the Canadian maritime provinces, Quebec, Ontario, Manitoba, and all U.S. states east of the Rockies except North Dakota, as well as in mountainous areas of Mexico below 4,900 feet (1,500 m). It is common in wooded areas, especially along lawn edges, as well as in exposed rocky areas, and in open fields and disturbed areas.
- Identification: Poison ivy can be found in any of the following three forms:
- as a trailing vine or groundcover that is 4 to 10 inches (10 to 25 cm) long;
- as a shrub that can grow up to 4 feet (1.2 meters) tall; and
- as a climbing vine that grows on trees or some other support, which may act as a tree limb.
Regardless of its form, alternating clusters of three almond-shaped leaves that range in color from light to dark green, turning red in the fall, easily distinguish poison ivy. Its leaf surfaces are smooth and become shiny with maturity, and their edges may or may not be ridged. Poison ivy vines have no thorns.
- Poison oak is a poisonous, upright shrub. Just as poison ivy merely resembles actual ivy, poison oak owes its name to a superficial resemblance to the oak tree’s leaves.
- Habitat: Poison oak comes in two region-based varieties:
- Atlantic poison oak, which can be found growing in forests, thickets, and dry, sandy fields; and
- Western poison oak, which is found only on the North American Pacific coast. It is typically found in damp, semi-shady areas near running water, but thrives in direct sunlight, and requires water only in early spring. The plant is common in Douglas fir forests and California oak woodlands. Poison oak vines climb far up the trunks of coastal redwoods, sometimes killing small trees.
- Identification: Due to its tendency to mimic its surroundings, identifying poison oak can be difficult. In open sunlight, it grows as a dense shrub, and as a climbing vine in shaded areas. Its leaves are somewhat larger than poison ivy leaves, although, similarly, poison oak displays an alternating three-leaf pattern. The leaves are hairy, scalloped and toothed, resembling real oak leaves, although they tend to be glossier. The leaf colors range from bronze to green, and red and pink in the fall. Poison oak’s small, round fruit emerges from white flowers. Once the leaves have shed in the winter, the plant may be identified by black marks where milky sap once cooled and dried.
- Poison sumac is a highly poisonous woody shrub or small tree. Although its rarity reduces the incidence of human exposure, the plant is far more virulent than other urushiol-secreting plants.
- Habitat: Poison sumac grows exclusively in wet soils, typically in peat bogs and swamps of the eastern United States and Canada.
Identification: Poison sumac is a shrub or small tree that can grow up to 20 feet (7 m) high. Unlike poison ivy and poison oak, poison sumac leaves come in long, paired rows with an additional leaf at the end. The leaves may have black spots made up of urushiol oil, which turns dark upon exposure to air. The fruits are semi-spherical, small and white, while non-poisonous sumac berries are red.
In summary, urushiol-secreting plants should be studied and prepared for to avoid painful allergic reactions. Inspectors should be aware of the outdoor foliage as they conduct their inspections, and wear long-sleeved shirts and pants to avoid the risk of exposure to poisonous plant life. Homeowners should also be aware of the plant species that may surround their homes, and take steps to remove those that threaten the health of family members.