An extremely itchy rash on the arms following yardwork


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A 34-year-old man presents with an itchy rash, primarily on his arms, but also, to a lesser extent, on his face. He denies any fever or malaise, and his medical history is unremarkable. He does not take any medications and notes that he spent the previous weekend doing yardwork on his property, and the rash appeared 4 days later. Physical examination reveals several linear arrangements of papulovesicles on the dorsal and ventral aspects of his forearms with surrounding erythema. 


Toxicodendron dermatitis, also known as Rhus dermatitis, is an allergic contact dermatitis resulting from exposure to urushiol, a resin found on the Toxicodendron family of plants. The most popular of these plants include poison ivy, poison oak, and poison sumac....

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Toxicodendron dermatitis, also known as Rhus dermatitis, is an allergic contact dermatitis resulting from exposure to urushiol, a resin found on the Toxicodendron family of plants. The most popular of these plants include poison ivy, poison oak, and poison sumac. The acute dermatitis, a type IV delayed hypersensitivity reaction, occurs after contact with the plant oil. Unless the allergen is immediately and thoroughly rinsed off, it can spread via contact from the original area of exposure to other parts of the skin. 

Toxicodendron exposure is a leading cause of allergic contact dermatitis in the United States.1 It is estimated that 50% to 70% of the population is susceptible to the reaction via casual contact with the plant. Of note, urushiol is also found in mangoes,2 Japanese lacquer trees, and cashews,3 and it can cause a similar rash in sensitive patients. 

The rash of toxicodendron dermatitis presents with erythema, papules, vesicles, and (sometimes) bullae, most notably in a linear distribution. The linear distribution results from the patient sweeping against the plant, as well as the spread of the resin from scratching. Exposed skin, such as on the arms and legs, is most notably involved. Papules are often in seen in interdigital webbing, on the wrists, and on the backs of the fingers. However, touching contaminated fingers to the face and groin transfers the resin and causes the characteristic vesicles to appear in those areas as well. Sometimes, black dots are seen within the rash; these represent black lacquer deposits resulting from the oxidized sap binding to the stratum corneum.4 

Uncommonly, if the leaves of these plants are burned and the smoke is inhaled, a systemic reaction may occur in the airways and lungs. A facial dermatitis with numerous small vesicles and swelling will likely also appear. 

Intense itching is usually the first reported symptom. The rash typically starts 1 to 3 days after the initial exposure, although it can be as soon as 8 hours later in highly sensitized individuals. New lesions can continue to appear up to 1 week later. 

Diagnosis of toxicodendron dermatitis is clinical and laboratory testing is not necessary. Patch testing for the allergen urushiol is not recommended, as it can induce a sensitivity in an otherwise nonsensitized individual. Other conditions that cause vesicles and should be considered in the differential diagnosis include bullous impetigo, non-plant-contact ­dermatitis, herpes virus, shingles, and phytophotodermatitis. 

Avoidance of the offending plant is the best prevention. If exposure to the plant is anticipated, wearing long sleeves, long pants tucked into footwear, and vinyl gloves can effectively act as a barrier. Urushiol binds to the lipid membranes of the cells within 10 to 20 minutes. Therefore, washing the skin thoroughly with soap and water within 20 minutes of exposure can eliminate or minimize the reaction. In addition, all exposed clothing and shoes should also be washed, as the urushiol oil can remain on inanimate objects for extended periods of time. 

Unless contraindicated, systemic corticosteroids such as oral prednisone are the most effective treatment in severe cases. The 1-week taper standard steroid dose packs, although convenient, are not ideal, as treatment is usually required for a full 2 to 3 weeks. Shorter treatment times are associated with higher rates of relapse of the dermatitis and pruritus. In milder cases, topical medium- to high-potency corticosteroids may be sufficient. Untreated, most cases resolve spontaneously within 3 weeks. 

Over-the-counter calamine lotion can be soothing for many patients. Oatmeal baths and cool compresses may also provide quick short-term relief. Patients should be educated, however, to avoid antihistamine ointments and topical anesthetic ointments,5 as these have the potential for further sensitization. 

The patient in our case was treated with 60 mg of prednisone daily for 1 week, followed by 40 mg daily for 1 week, and finally 20 mg daily for 1 week. At the 4-week follow-up, he reported complete resolution of the rash and resolution of the itching with no signs of recurrence.

Esther Stern, NP, is a family nurse practitioner at Advanced Dermatology & Skin Surgery, P.C., in Lakewood, N.J.


  1. Paller AS, Mancini AJ. Hurwitz Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood and Adolescence. 4th ed. Philadelphia, PA: Elsevier Saunders; 2011.
  2. Catalano PN. Mango sap and poison ivy dermatitis. J Am Acad Dermatol. 1984;10:522.
  3. Marks JG Jr, DeMelfi T, McCarthy MA, et al. Dermatitis from cashew nuts. J Am Acad Dermatol. 1984;10:627-631.
  4. Mallory SB, Miller OF, Tyler WB. Toxicodendron radicans dermatitis with black lacquer deposit on the skin. J Am Acad Dermatol. 1982;6:363-368.
  5. James WD, Berger TG, Elston DM. Andrews’ Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, PA: Saunders-Elsevier; 2011. 
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