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This article originally appeared in the September 1996 FDA Consumer. |
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![[illustrations of poison ivy, poison sumac, and poison oak]](/peth04/20041108131555im_/http://www.fda.gov/fdac/graphics/1996graphics/poisnivy.gif)
Pamela Lillian Isley can manipulate plants in unexplained ways. They bend to her will, growing and threatening the environment and society--at least in Gotham City. In the world of Batman, the fictional Isley is better known as the beautiful criminal Poison Ivy. Her alias is fitting. Just as she is the bane of Batman's existence, in the real world the poison ivy plant--along with its cousins poison oak and poison sumac--is the bane of millions of campers, hikers, gardeners, and others who enjoy the great outdoors.
Approximately 85 percent of the population will develop an allergic reaction if exposed to poison ivy, oak or sumac, according to the American Academy of Dermatology. Nearly one-third of forestry workers and firefighters who battle forest fires in California, Oregon and Washington develop rashes or lung irritations from contact with poison oak, which is the most common of the three in those states.
Usually, people develop a sensitivity to poison ivy, oak or sumac only after several encounters with the plants, sometimes over many years. However, sensitivity may occur after only one exposure.
The cause of the rash, blisters, and infamous itch is urushiol (pronounced oo-roo-shee-ohl), a chemical in the sap of poison ivy, oak and sumac plants. Because urushiol is inside the plant, brushing against an intact plant will not cause a reaction. But undamaged plants are rare.
"Poison oak, ivy and sumac are very fragile plants," says William L. Epstein, M.D., professor of dermatology, University of California, San Francisco. Stems or leaves broken by the wind or animals, and even the tiny holes made by chewing insects, can release urushiol.
Reactions, treatments and preventive measures are the same for all three poison plants. Avoiding direct contact with the plants reduces the risk but doesn't guarantee against a reaction. Urushiol can stick to pets, garden tools, balls, or anything it comes in contact with. If the urushiol isn't washed off those objects or animals, just touching them--for example, picking up a ball or petting a dog--could cause a reaction in a susceptible person. (Animals, except for a few higher primates, are not sensitive to urushiol.)
Urushiol that's rubbed off the plants onto other things can remain potent for years, depending on the environment. If the contaminated object is in a dry environment, the potency of the urushiol can last for decades, says Epstein. Even if the environment is warm and moist, the urushiol could still cause a reaction a year later.
"One of the stories I tell people is of the hunter who gets poison oak on his hunting coat," says Epstein. "He puts it on a year later to go hunting and gets a rash [from the urushiol still on the coat]."
Almost all parts of the body are vulnerable to the sticky urushiol, producing the characteristic linear (in a line) rash. Because the urushiol must penetrate the skin to cause a reaction, places where the skin is thick, such as the soles of the feet and the palms of the hands, are less sensitive to the sap than areas where the skin is thinner. The severity of the reaction may also depend on how big a dose of urushiol the person got.
Because urushiol can penetrate the skin within minutes, there's no time to waste if you know you've been exposed. "The earlier you cleanse the skin, the greater the chance that you can remove the urushiol before it gets attached to the skin," says Hon-Sum Ko, M.D., an allergist and immunologist with FDA's Center for Drug Evaluation and Research. Cleansing may not stop the initial outbreak of the rash if more than 10 minutes has elapsed, but it can help prevent further spread.
If you've been exposed to poison ivy, oak or sumac, if possible, stay outdoors until you complete the first two steps:
If you don't cleanse quickly enough, or your skin is so sensitive that cleansing didn't help, redness and swelling will appear in about 12 to 48 hours. Blisters and itching will follow. For those rare people who react after their very first exposure, the rash appears after seven to 10 days.
Because they don't contain urushiol, the oozing blisters are not contagious nor can the fluid cause further spread on the affected person's body. Nevertheless, Epstein advises against scratching the blisters because fingernails may carry germs that could cause an infection.
The rash will only occur where urushiol has touched the skin; it doesn't spread throughout the body. However, the rash may seem to spread if it appears over time instead of all at once. This is either because the urushiol is absorbed at different rates in different parts of the body or because of repeated exposure to contaminated objects or urushiol trapped under the fingernails.
The rash, blisters and itch normally disappear in 14 to 20 days without any treatment. But few can handle the itch without some relief. For mild cases, wet compresses or soaking in cool water may be effective. Oral antihistamines can also relieve itching.
FDA also considers over-the-counter topical corticosteroids (commonly called hydrocortisones under brand names such as Cortaid and Lanacort) safe and effective for temporary relief of itching associated with poison ivy.
For severe cases, prescription topical corticosteroid drugs can halt the reaction, but only if treatment begins within a few hours of exposure. "After the blisters form, the [topical] steroid isn't going to do much," says Epstein. The American Academy of Dermatology recommends that people who have had severe reactions in the past should contact a dermatologist as soon as possible after a new exposure.
Severe reactions can be treated with prescription oral corticosteroids. Phillip M. Williford, M.D., assistant professor of dermatology, Wake Forest University, prescribes oral corticosteroids if the rash is on the face, genitals, or covers more than 30 percent of the body. The drug must be taken for at least 14 days, and preferably over a three-week period, says FDA's Ko. Shorter courses of treatment, he warns, will cause a rebound with an even more severe rash.
There are a number of OTC products to help dry up the oozing blisters, including:
Desensitization, vaccines, and barrier creams have been studied over the last several decades for their potential to protect against poison ivy reactions, but none have been approved by FDA for this purpose.
Right now, prevention seems the best treatment, unless you plan to take lessons from Batman's bane with Poison Ivy's name.
Isadora B. Stehlin is a member of FDA's public affairs staff.
Poison ivy, oak and sumac are most dangerous in the spring and summer, when there is plenty of sap, the urushiol content is high, and the plants are easily bruised. However, the danger doesn't disappear over the winter. Dormant plants can still cause reactions, and cases have been reported in people who used the twigs of the plant for firewood or the vines for Christmas wreaths. Even dead plants can cause a reaction, because urushiol remains active for several years after the plant dies.
If poison ivy invades your yard, "there's really no good news for you," says David Yost, a horticulturist (specialist in fruits, vegetables, flowers, and general gardening) with the state of Virginia. The two herbicides most commonly used for poison ivy--Roundup and Ortho Poison Ivy Killer--will kill other plants as well. Spraying Roundup (active ingredient glyphosate) on the foliage of young plants will kill the poison ivy, but if the poison ivy vine is growing up your prize rhododendron or azalea, for example, the Roundup will kill them too, he says.
Ortho Poison Ivy Killer (active ingredient triclopyr), if used sparingly, will kill poison ivy but not trees it grows around, says Joseph Neal, Ph.D., associate professor of weed science, Cornell University. "But don't use it around shrubs, broadleaf ground cover, or herbaceous garden plants," he says. Neal explains it is possible to spray the poison ivy without killing other plants if you pull the poison ivy vines away from the desirable plants and wipe the ivy foliage with the herbicide, or use a shield on the sprayer to direct the chemical.
If you don't want to use chemicals, "manual removal will get rid of the ivy if you're diligent," says Neal. You must get every bit of the plant--leaves, vines, and roots--or it will sprout again.
The plants should be thrown away according to your municipality's regulations, says Neal. Although urushiol will break down with composting, Neal doesn't recommend that because the plants must be chopped into small pieces first, which just adds to the time you're exposed to the plant and risk of a rash. "It's a health issue," he says.
Never burn the plants. The urushiol can spread in the smoke and cause serious lung irritation.
The American Academy of Dermatology recommends that whenever you're going to be around poison ivy--trying to clear it from your yard or hiking in the woods--you wear long pants and long sleeves and, if possible, gloves and boots.
Neal recommends wearing plastic gloves over cotton gloves when pulling the plants. Plastic alone isn't enough because the plastic rips, and cotton alone won't work because after a while the urushiol will soak through.
--I.B.S.
Unfortunately, poison ivy, oak and sumac don't grow with little picture ID badges around their stems, so you have to know what to look for. The famous rule "leaves of three, let it be" is good to follow, except that some of the plants don't always play by the rules and have leaves in groups of five to nine. To avoid these plants and their itchy consequences, here's what to look for.
--I.B.S.