With summer temperatures luring us outdoors, scientists with the Weed Science Society of America (WSSA) say it’s a great time for refresher course on poison oak, poison ivy and poison sumac. All three thrive during summer months and are known to trigger highly irritating skin rashes that can last for many days.
“When you look at the thousands of people exposed each year and at the misery a rash can produce, poison oak, poison ivy and poison sumac certainly rank among the most notorious weeds in the nation,” says Lee Van Wychen, Ph.D., WSSA science policy director.
All three belong to the Toxicodendron genus and produce irritating urushiol oils. When urushiol comes in contact with the skin of sensitive individuals, itching and watery blisters will follow.
Poison oak and poison ivy in particular are common fixtures in many outdoor landscapes, often tucked among other native vegetation and growing as either a low shrub or trailing vine. Both produce small, whitish green flowers in the spring, followed by small berries in the summer. Birds enjoy the seeds and help to spread the weeds into new areas.
Poison sumac is rarer, and tends to be found primarily in wetlands. This characteristic is one of several differences among the three weed species and where they are found.
Poison oak grows as a low shrub in eastern and southern states and in tall clumps or long vines on the Pacific Coast. Fuzzy green leaves grow in clusters of three. It may have yellow or green flowers and clusters of green-yellow or white berries.
Poison ivy is found nationwide, with the exception of Alaska, Hawaii and some portions of the western coastline. Each leaf includes three glossy leaflets that vary in color (and sometimes shape) throughout the year – red in spring, green in summer and yellow, orange or red in the fall. It can grow as a shrub or as hairy, ropelike vines sometimes seen growing up the sides of trees.
Poison sumac grows as a woody shrub or small tree primarily in the eastern half of the U.S. Leaves feature multiple pairs of leaflets that have a smooth, velvet-like texture. Flowers and fruit are similar to those produced by poison oak or poison ivy, but hang in loose clusters.
Misinformation about poison oak, poison ivy and poison sumac abounds, making it important to separate fact from fiction.
Fiction: Only the leaves are toxic. Fact: All parts of the plants can trigger an allergic response, including the leaves, roots, flowers, berries, stems and vines.
Fiction: The painful rash can be spread through watery fluid found in blisters. Fact: Only exposure to the oily toxin urushiol will trigger a reaction – not the fluid in blisters. Rashes often emerge over a series of days, though, which can make it seem as though they are spreading as blisters ooze.
Fiction: If you don’t touch the plants directly, you’re in the clear. Fact: Toxic oils can linger on clothes, gardening gloves, tools, shoes and even pet fur – producing a skin rash just as if you touched the plant yourself. Wash your tools, clothing and pets regularly, especially after an exposure. The oils can remain potent for months and even years.
Fiction: You can dispose of poison oak, poison ivy and poison sumac just as you would any other weed. Fact: It is important to take great care in disposing of plants that you pull, mow or dig. You don’t want yourself or others to be exposed to oily toxins that remain. Be especially careful to never use burning as a disposal strategy. Inhaling the smoke can cause a whole-body reaction.
Fiction: There is nothing I can do to avoid a rash if I’ve touched poison oak, poison ivy or poison sumac. Fact: You may be able to avoid a rash or reduce its severity by pouring rubbing alcohol over the exposed area as soon as possible and washing with running water. Clinical tests show that dishwashing detergent is also effective at removing the rash-causing urushiol toxin.
Fiction: Some people are simply immune to urushiol-induced rashes. Fact: While it is true some individuals are not bothered by a rash, sensitivity to urushiol can develop at any time. Once you’ve had a rash, you can become more sensitive and have a stronger allergic response the next time you are exposed.
“Prevention is paramount when it comes to poison oak, poison ivy and poison sumac,” Van Wychen says. “If you plan to work or play in an area where it may be growing, wear protective clothing, including long sleeves and long pants tucked into your boots or hiking shoes. Being a bit warm may be a better alternative than days of suffering from a painful rash.”
For more information about poison oak, poison ivy and poison sumac, visit www.cdc.gov/niosh/topics/plants.
About the Weed Science Society of America
The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Society promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, fosters awareness of weeds and their impact on managed and natural ecosystems, and promotes cooperation among weed science organizations across the nation and around the world. For more information, visit www.wssa.net.