Poison Ivy

A 13 year old boy comes to the office with the complaint of an itchy rash on his arms, legs, and trunk. He has just returned from a camping trip in Michigan. He says that he wore short sleeves and shorts and always had a shirt on. The rash has areas of linear vesicles.

What is the diagnosis and how would you treat this boy?

  •  Urushiol-induced contact dermatitis (also called Toxicodendron dermatitis and Rhus dermatitis) is an allergic contact dermatitis (allergic phytodermatitis) that occurs from exposure to members of the plant genus Toxicodendron which contain the irritant chemical urushiol . In North America, this includes poison ivy, poison oak, and, much less frequently, poison sumac. Although technically not Toxicodendron species, the irritant chemical (urushiol) is also found in mangoes and Japanese lacquer trees and can incite a similar clinical picture. A large number of other botanicals.
  • Toxicodendron species are abundant throughout the United States except in desert areas, elevations above 4000 ft, Alaska, or Hawaii. Poison oak is most common west of the Rockies, poison ivy to the east, and poison Sumac in the southeast. Approximately 50-70% of the US population is susceptible if exposed casually; however, this percentage increases with significant exposure. Approximately 10-15% of the population is extremely sensitive. Toxicodendron dermatitis is the most common cause of contact dermatitis in the United States, exceeding all other causes combined.
  • The reaction occurs after contact with the damaged plant that releases the sap like material which binds strongly to the skin. Unless washed off within a few minutes after contact, a reaction will occur.
  • Toxicodendron species contain oleoresins known collectively as urushiol. In susceptible individuals, these compounds trigger a type IV delayed hypersensitivity reaction. Usually, the skin is involved; however, the eyes, airway, and lungs may be involved if exposed to smoke from burning plants. Reactions from gastrointestinal exposure in the form of urushiol-containing homeopathic remedies have also been reported
  • The greater the sensitivity to the antigen, the sooner and more extensive the reaction. Touching areas of contact can spread the material to other parts of the body that were not initially in contact with the sap and it is important to scrub under the fingernails after contact.

Clinical Manifestations

  •  In susceptible individuals, lesions generally appear within 12-48 hours, although they have been noted to appear earlier. New lesions may continue to appear for up to 2-3 weeks.  Initially, these lesions tend to occur from the slow reaction to adsorbed urushiol; however, lesions that appear later are often secondary to contact with contaminated surfaces.
  • Initially there is pruritis followed by erythema, edema, papules, vesicles, and bullae.Helpful in diagnosing the rash is the linear distribution caused by the branches brushing the area of contact. 
  • Scratching the rash will help spread the lesions and there may be areas of rash where the skin was protected by clothing.
  • Contrary to popular belief, the fluid from vesicles and bulla do not spread the rash. 
  • The rash can be spread from contact with fomites like shoes, clothing, tools, and from the smoke from burning plants. Animal fur can also be reservoirs of the sap and pets can help spread the antigen if they have been in contact with the plants.
  • Complete resolution is expected within 7-21 days.


  • Immediate decontamination.  Urushiol penetrates the skin and binds to membrane lipids within 10-20 minutes of contact. If the toxin can be removed before this occurs, reaction can be avoided.
  • Washing exposed areas with copious amounts of water within 20 minutes of exposure has been shown to reduce reactivity. Copious water is recommended because soaps can spread the urushiol oil around the skin.  The efficacy of washing appears to decrease over time.
  • Clean clothes and any other objects that might have been in contact with the oils.
  • Domeboro, calamine lotion, oatmeal baths, and Burow solution, can be used for symptomatic relief.
  •  Low-dose steroids and topical antihistamines have not been shown to have any beneficial effect.
  • Topical steroids are useful for mild cases.
  • May need oral steroids for 1-2 weeks. Full dosage for the first week and then taper the second week to prevent rebound
  • Cut the patient's nails
  • Cool compresses may give some relief
  • Oral antihistamines can be of some benefit for the relief of pruritus, especially in severe cases with urticarial lesions accompanying the bullae.
  •  Topical products such as IvyBlock may prevent some allergic reactions by providing an invisible barrier.  Useful if known sensitive individual is going to area known to have poison ivy.


  1. Tunnessen, Walter W.Jr. Poisonivy, oak, and sumac: The three witches of summer.Contemporary Pediatrics June 1985
  2. Epstein, Guin, and Mallach  A Poison Ivy Update  Contemporary Pediatrics April 2000
  3. Gladman A. Toxicodendron Dermatitis:Poison Ivy, Oak, and Sumac.  Wilderness and Environmental Medicine. 17,120-128 (2006)
  4. Tanner T, Rhus (Toxicodendron) Dermatitis.  Primary Care: Clinics in Office Practice. Vol 27, issue 2. June 2000
  5. Botanical dermatology: allergic contact dermatitis. Electronic Textbook of Dermatology. Available at Accessed June 16, 2007.
  6. Cardinali C, Francalanci S, Giomi B, et al. Contact dermatitis from Rhus toxicodendron in a homeopathic remedy. J Am Acad Dermatol. Jan 2004;50(1):150-1. [Medline].
  1.  (10/3/2010) S. Stephanides and C. MoorePlant Poisoning, Toxicodendron: Treatment & Medication accessed (10/03/2010)