Rhus Dermatitis

Aka: Rhus Dermatitis, Poison Ivy, Poison Ivy Dermatitis, Poison Oak, Poison Sumac, Toxicodendron radicans, Rhus toxicodendron, Urushiol

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II. Epidemiology

  1. Prevalence of complete Rhus Immunity: 10-15%
  2. Prevalence Rhus Allergy: Total of 75-85% of U.S. Adults
    1. Consistent Reaction: 50% of U.S. Adults
    2. Reaction to high doses: 25-35% of U.S. Adults

III. Pathophysiology

  1. Allergic Contact Dermatitis to Rhus Group of Plants
    1. Poison Oak (West of the Rocky Mountains)
    2. Poison Ivy (East of the Rocky Mountains)
    3. Poison Sumac (Swampy areas in Florida, Northeast)
  2. Hypersensitivity Reaction to Urushiol oil
    1. Sensitivity to one plant confers sensitivity to all
    2. Oil leaks out from damaged plant
    3. Oil evaporates from skin within 4 hours
    4. Oil evaporates much more slowly from fomites (years in some cases)
      1. Garments
      2. Animal hair (cat, dog)
      3. Ash in smoke from burning leaves
  3. Recurrent Eruption is not related to Vesicle leakage
    1. Vesicles have sterile (non Rhus) content
    2. Repeat eruption is related to re-inoculation
    3. See description of slower oil evaporation above

IV. Symptoms

  1. Very pruritic rash

V. Signs

  1. Papulovesicular Dermatitis
    1. Linear formation (associated with Rhus oil spread)
  2. Inhalational reaction may also occur
    1. Burned Poison Ivy leaves (e.g. brush clearing) can result in significant airway inflammation

VI. Differential Diagnosis

  1. Irritant Contact Dermatitis
  2. Allergic Contact Dermatitis
  3. Viral Exanthem
  4. Impetigo (superinfected excoriations)
  5. Photocontact Dermatitis
    1. Contrast with Rhus airborne Contact Dermatitis
    2. Does not affect some airborne Rhus areas
      1. Retroauricular folds
      2. Submental folds
      3. Nasolabial folds

VII. Management

  1. Symptomatic Treatment (sooth and dry weeping lesions)
    1. Cool compresses for 15-20 minutes per hour
    2. Topicals
      1. Colloidal Oatmeal Bath (Aveeno bath)
      2. Calamine lotion applied several times per day
      3. Burow's Solution (Topical astringent, e.g. Domeboro)
      4. Topical Analgesics (e.g. Menthol, camphor)
        1. Avoid Topical Anesthetics (e.g. topical Diphenhydramine, topical Lidocaine or benzocaine)
    3. Antihistamines tend to offer minimal relief
      1. Atarax at bedtime for Pruritus may help with sleep and sedation
      2. Oral Antihistamines fail to offer benefit as Histamines are not central to Rhus Dermatitis related Pruritus
      3. Do NOT use topical Antihistamines (skin sensitizers)
  2. Corticosteroid
    1. Topical Corticosteroids (for Mild to Moderate Localized Involvement)
      1. Strong Topical Corticosteroids (e.g. Clobetasol or Temovate gel, soothing if refrigerated)
      2. Avoid Hydrocortisone and other inadequately weak Topical Corticosteroids
      3. Most effective prior to Vesicle formation
      4. Use ointment for very dry lesions
    2. Systemic Corticosteroids (for severe cases)
      1. Indications
        1. Severe, Widespread involvement (esp. >20% of body)
        2. Sensitive region involvement (e.g. periorbital or genital lesions)
      2. Avoid short courses (e.g. medrol dose pack) due to rebound worsening
        1. Curtis (2014) J Clin Med Res 6(6):429-34 +PMID:25247016 [PubMed]
      3. Adults
        1. Start: Prednisone 60 mg orally per day divided doses
        2. Taper: Decrease by 10 mg every third day x18 days
      4. Children
        1. Start: Prednisone 0.5 - 1 mg/kg/day to 40-60 mg/day
        2. Taper by 5 mg every three days over 18 days
    3. Supersensitive patient early in recurrence (<12 hour)
      1. Triamcinolone 40-60 mg IM or
      2. Combination
        1. Betamethasone 12 mg IM (short acting) AND
        2. Methylprednisolone 40 mg IM (long acting)
  3. Antibiotics
    1. Indicated for signs of superinfection
    2. Mild: Topical Antibiotics
    3. Severe: Oral Antibiotics

VIII. Course

  1. Mild, delayed reaction in 90% patients
    1. Pruritic papulovesicular lesions form over 1-2 days
    2. Resolves over 10 to 14 days
  2. Severe reaction in 10% of patients
    1. Onset of debilitating rash over 4 to 8 hours

IX. Prevention

  1. Washing off oil immediately (within 10 minutes) may prevent rash
    1. Soap and Water (preferred)
      1. Scrub for several minutes to remove oils
    2. Solvents poured over area
      1. No evidence for higher efficacy than cheap and effective soap and water
      2. Products
        1. Tecnu Outdoor Skin Cleanser (or Zanfel)
        2. Other non-specific solvents
          1. Acetone
          2. Rubbing Alcohol (Isopropyl Alcohol)
          3. Anecdotally Gasoline has been used, but causes significant Burn Injury and is NOT recommended
      3. Do not dab on solvent (e.g. Alcohol pad, towelettes)
        1. Spreads Rhus oil
      4. Use Solvents only when ready to travel home
        1. Removes lipid protective skin coating
        2. Can predispose to worse second Rhus exposure
  2. Clean all contaminated clothing, shoes, and linens
    1. Urushiol oil can remain on unwashed items for years
    2. Launder washables
    3. Use Solvents above for non-washables
  3. Consider Ivy Block (e.g. Ivy X Pre-Contact) applied to skin prior to exposure
    1. Variable efficacy and not typically recommended (unproven efficacy)
  4. Wash pets
  5. Identify plants to avoid
  6. Wear protective clothing when hiking in weed areas

X. References

  1. (2013) Presc Lett 20(8): 46
  2. (2023) Presc Lett 30(6): 33
  3. Baer (1990) Cutis 46:34-6 [PubMed]
  4. Gayer (1988) Cutis 42:99-100 [PubMed]
  5. Epstein (1991) J Wilderness Med 2:183-6 [PubMed]

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