| Poison ivy | |
|---|---|
 | |
| Toxicodendron radicans in autumn | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Sapindales |
| Family: | Anacardiaceae |
| Subfamily: | Anacardioideae |
| Genus: | Toxicodendron |
| Species | |
T. orientaleGreene | |
Poison ivy is a type of allergenic plant in the genusToxicodendron native to Asia and North America. Formerly considered a single species,Toxicodendron radicans, poison ivies are now generally treated as a complex of three separate species:T. radicans,T. rydbergii, andT. orientale. They are well known for causingurushiol-induced contact dermatitis, an itchy, irritating, and sometimes painful rash, in most people who touch them. The rash is caused byurushiol, a clear liquid compound in the plant'ssap. They are variable in appearance and habit, and despite its common name, it is not a "true" ivy (Hedera), but rather a member of thecashew andpistachio family (Anacardiaceae).T. radicans is commonly eaten by many animals, and the seeds are consumed by birds, but poison ivy is most often thought of as an unwelcomeweed.
Three species of poison ivy are generally recognised; they are sometimes considered subspecies ofToxicodendron radicans:[1][2][3]
Poison ivies can grow as small plants, shrubs, or climbing vines.[4] They are commonly characterized by clusters of leaves, each containing three leaflets,[4] hence the common expression "leaves of three, let it be".[5] These leaves can vary between an elliptic to egg shape and will have either smooth, lobed, or toothedmargins. Additionally, the leaf clusters arealternate on the stem. Clusters of small, greenish flowers bloom from May to July and produce white berries in the fall a few millimeters in diameter.[6]
Urushiol-induced contact dermatitis is theallergic reaction caused by poison ivy. In extreme cases, a reaction can progress toanaphylaxis. Around 15 to 25 percent of people have no allergic reaction to urushiol, but most people have a greater reaction with repeated or more concentrated exposure.[7][8]
Over 350,000 people are affected by urushiol annually in the United States.[9]
The oozing fluids released by scratching blisters do not spread the poison. The fluid in the blisters is produced by the body and it is not urushiol itself.[10] The appearance of a spreading rash indicates that some areas received more of the poison and reacted sooner than other areas or that contamination is still occurring from contact with objects to which the original poison was spread.[citation needed]
Those affected can unknowingly spread the urushiol inside the house, on phones, door knobs, couches, counters, desks, and so on, thus in fact repeatedly coming into contact with poison ivy and extending the length of time of the rash. If this happens, the surfaces should be wiped with bleach or a commercial urushiol removal agent. The blisters and oozing result from blood vessels that develop gaps and leak fluid through the skin; if the skin is cooled, the vessels constrict and leak less.[11] If plant material with urushiol is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty.[10] If poison ivy is eaten, the mucus lining of the mouth and digestive tract can be damaged.[12]
Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction. In addition, oil transferred from the plant to other objects (such as pet fur) can cause the rash if it comes into contact with the skin.[13][10] Clothing, tools, and other objects that have been exposed to oil should be washed to prevent further reactions.[14]
Immediate washing with soap and cold water orrubbing alcohol may help prevent a reaction.[15] During a reaction, calamine lotion ordiphenhydramine may help mitigate symptoms.Corticosteroids, either applied to the skin or taken by mouth, may be appropriate in extreme cases. An astringent containing aluminum acetate (such asBurow's solution) may also provide relief and soothe the uncomfortable symptoms of the rash.[16]
Urushiol binds to the skin on contact where it causes severe itching that develops into reddish inflammation or uncoloured bumps, and thenblistering. Theselesions may be treated withcalamine lotion,Burow's solution compresses, dedicated commercial poison ivy itch creams, or baths to relieve discomfort,[17] though recent studies have shown some traditional medicines to be ineffective.[18][19]Over-the-counter products to ease itching—or simply oatmeal baths andbaking soda—are now recommended bydermatologists for the treatment of poison ivy.[20]
A plant-based remedy cited to counter urushiol-induced contact dermatitis isjewelweed, though jewelweed extracts had no positive effect in clinical studies.[21][22][23][24] Others argue that prevention of lesions is easy if one practices effective washing, using plain soap, scrubbing with a washcloth, and rinsing three times within 2–8 hours of exposure.[25]
The pentadecylcatechols of theoleoresin within the sap of poison ivy and related plants causes the allergic reaction; the plants produce a mixture of pentadecylcatechols, which collectively is called urushiol. After injury, the sap leaks to the surface of the plant where the urushiol becomes a blackishlacquer after contact with oxygen.[26][27]
Typically, the rash from the urushiol oil lasts about five to twelve days, but in extreme cases it can last a month or more.[28] A urushiol rash usually develops within a week of exposure and can last 1–4 weeks, depending on severity and treatment. In rare cases, urushiol reactions may require hospitalization.[10]
People who are sensitive to urushiol can also experience a similar rash frommangoes. Mangoes are in the same family (Anacardiaceae) as poison ivy; the sap of the mango tree and skin of mangoes has a chemical compound similar to urushiol.[29] A related allergenic compound is present in the raw shells ofcashews.[30] Similar reactions have been reported occasionally from contact with the related fragrant sumac (Rhus aromatica) andJapanese lacquer tree. These other plants are also in the family Anacardiaceae.[citation needed]