Poison ivy

Three species of poison ivy are generally recognised; they are sometimes considered subspecies of Toxicodendron radicans:[1][2][3]

• Toxicodendron orientale: found in East Asia.[4]
• Toxicodendron radicans: found throughout eastern Canada and the United States, Mexico and Central America, Bermuda and the Bahamas.[4]
• Toxicodendron rydbergii: found throughout Canada and much of the United States except the southeast.[4]

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 toothed margins. Additionally, the leaf clusters are alternate 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]

• 
  T. radicans vine with typical reddish "hairs"
• 
  Flower detail, with bee
• 
  Poison ivy on a roadside
• 
  Leaves may be smooth or notched on the same plant.

Blisters from contact with poison ivy

Urushiol-induced contact dermatitis is the allergic reaction caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis. 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.

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 has happened, wipe down the surfaces 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]

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]

• Gluta spp (rengas tree)
• Lithraea molleoides (aruera – South America)
• Smodingium argutum (African poison ivy)
• Toxicodendron pubescens (poison oak – eastern)
• Toxicodendron diversilobum (poison oak – western)
• Toxicodendron vernix (poison sumac)
• Toxicodendron vernicifluum (Japanese lacquer tree)[31]

• Site with extensive photo images of plants and skin rashes