UMEM Educational Pearls

Category: Toxicology

Title: "Leaves of 3 let them be"

Keywords: Poison Ivy, Toxicodendron, Urushiol (PubMed Search)

Posted: 10/6/2016 by Kathy Prybys, MD (Emailed: 10/7/2016) (Updated: 10/7/2016)
Click here to contact Kathy Prybys, MD


Fall clean up = Poison Ivy, oak, sumac (Toxicodendron species) which is ubiquitous in North America but it can also be found in British Columbia, Mexico and in parts of Asia. These plants are truly the scourge of outdoor enthusiasts and agricultural workers responsible for up to 40 million cases of miserable often temporarily incapacitating rashes annually.

Fast Facts:

  • Grows as plant, vine, or shrub with leaves ranging in color from light or glossy green to red and yellow in fall.
  • Exposure by direct contact with plant, indirectly from oil resin on objects, clothes, pets, or airborne from burning plant.
  • Urushiol toxin induced type IV hypersensitivity allergic contact dermatitis. This oily resin toxin is excreted from all parts of plant (stems, leaves, flowers, roots, vines). and is extremely stable staying active even after plant dies.
  • Intensely itchy blistering rash starts 12-72 hours after contact and lasts up to 21 days. Characterized by red streaks or linear configuration where skin brushed up against plant sap. Inflammation (redness, swelling, hives, blistering) to thick leathery plagues depending on severity and vulnerability of skin location. Intense inflammation can mimic cellulitis.
  • Rash is Not contagious but spread of oil on clothes, pets, tools, objects is!
  • Delayed reaction accounts for seemingly "spread" of rash. Eruption rate depends on thickness of skin and dose of urushiol oil.

Treatment Tips:

  • Prevention. Avoidance and universal precautions when gardening. Clusters of 3 leaves each trio growing on their own stem, hairy vines, no thorns, white berries.
  • Cover skin to prevent exposure and if known contact immediately wash skin, clothes, objects.
  • Hot water relieves itch as does cool compresses.
  • Domeboro or witch hazel are astringents can reduce inflammation.
  • External analgesics (e.g., benzocaine, lidocaine, benzyl alcohol) can help itching.
  • Highly viscous or granular cream surfactant washes bind urushiol and can reduce exposure. Zanfel, Mean green, Gojo orange, various generic poison ivy removal scrubs now available. (Zanfel works wonders used every few hours and may alleviate need for steroids but is $$$ and several tubes are required).
  • In severe cases, Steriod burst followed by 2-3 week taper to prevent relapse flare.



Toxicodendron dermatitis:poison ivy,oak, sumac. Gladman AC. Wilderness Environ Med. 2006. Summer ;17(2):120-8.

Compositions and methods for removing urushiol and treating resulting skin condition.

US 7858570 B2


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