II. Epidemiology
- Prevalence of complete Rhus Immunity: 10-15%
-
Prevalence Rhus Allergy: Total of 75-85% of U.S. Adults
- Consistent Reaction: 50% of U.S. Adults
- Reaction to high doses: 25-35% of U.S. Adults
III. Pathophysiology
-
Allergic Contact Dermatitis to Rhus Group of Plants
- Poison Oak (West of the Rocky Mountains)
- Poison Ivy (East of the Rocky Mountains)
- Poison Sumac (Swampy areas in Florida, Northeast)
-
Hypersensitivity Reaction to Urushiol oil
- Sensitivity to one plant confers sensitivity to all
- Oil leaks out from damaged plant
- Oil evaporates from skin within 4 hours
- Oil evaporates much more slowly from fomites (years in some cases)
- Garments
- Animal hair (cat, dog)
- Ash in smoke from burning leaves
- Recurrent Eruption is not related to Vesicle leakage
- Vesicles have sterile (non Rhus) content
- Repeat eruption is related to re-inoculation
- See description of slower oil evaporation above
IV. Symptoms
- Very pruritic rash
V. Signs
- Papulovesicular Dermatitis
- Linear formation (associated with Rhus oil spread)
- Inhalational reaction may also occur
- Burned Poison Ivy leaves (e.g. brush clearing) can result in significant airway inflammation
VI. Differential Diagnosis
- Irritant Contact Dermatitis
- Allergic Contact Dermatitis
- Viral Exanthem
- Impetigo (superinfected excoriations)
-
Photocontact Dermatitis
- Contrast with Rhus airborne Contact Dermatitis
- Does not affect some airborne Rhus areas
- Retroauricular folds
- Submental folds
- Nasolabial folds
VII. Management
- Symptomatic Treatment (sooth and dry weeping lesions)
- Cool compresses for 15-20 minutes per hour
- Colloidal Oatmeal Bath (Aveeno bath)
- Calamine lotion applied several times per day
- Burow's Solution
- Antihistamines tend to offer minimal relief
- Atarax at bedtime for Pruritus may help with sleep and sedation
- Oral Antihistamines fail to offer benefit as histamines are not central to Rhus Dermatitis related Pruritus
- Do NOT use topical Antihistamines (skin sensitizers)
-
Corticosteroid
- Topical for Mild to Moderate Localized Involvement
- Strong Topical Corticosteroids (e.g. Clobetasol or Temovate gel, soothing if refrigerated)
- Avoid Hydrocortisone and other inadequately weak Topical Corticosteroids
- Most effective prior to Vesicle formation
- Use ointment for very dry lesions
- Systemic for Severe, Widespread or Periorbital Lesion
- Avoid short courses due to rebound worsening
- Adults
- Start: Prednisone 60 mg orally per day divided doses
- Taper: Decrease by 10 mg every third day x18 days
- Children
- Start: Prednisone 0.5 - 1 mg/kg/day to 40-60 mg/day
- Taper by 5 mg every three days over 18 days
- Supersensitive patient early in recurrence (<12 hour)
- Triamcinolone 40-60 mg IM or
- Combination
- Betamethasone 12 mg IM (short acting) AND
- Methylprednisolone 40 mg IM (long acting)
- Topical for Mild to Moderate Localized Involvement
- Antibiotics
- Indicated for signs of superinfection
- Mild: Topical Antibiotics
- Severe: Oral Antibiotics
VIII. Course
- Mild, delayed reaction in 90% patients
- Pruritic papulovesicular lesions form over 1-2 days
- Resolves over 10 to 14 days
- Severe reaction in 10% of patients
- Onset of debilitating rash over 4 to 8 hours
IX. Prevention
- Washing off oil immediately (within 10 minutes) may prevent rash
- Soap and Water
- Scrub for several minutes to remove oils
- Solvents poured over area (no evidence for higher efficacy than the cheaper soap and water)
- Tecnu Outdoor Skin Cleanser (or Zanfel)
- Other non-specific solvents
- Acetone
- Rubbing Alcohol (Isopropyl Alcohol)
- Anecdotally Gasoline has been used, but causes significant Burn Injury and is NOT recommended
- Do not dab on solvent (e.g. Alcohol pad, towelettes)
- Spreads Rhus oil
- Use Solvents only when ready to travel home
- Removes lipid protective skin coating
- Can predispose to worse second Rhus exposure
- Soap and Water
- Clean all contaminated clothing, shoes, and linens
- Urushiol oil can remain on unwashed items for years
- Launder washables
- Use Solvents above for non-washables
- Consider Ivy Block (e.g. Ivy X Pre-Contact) applied to skin prior to exposure
- Variable efficacy and not typically recommended
- Wash pets
- Identify plants to avoid
- Wear protective clothing when hiking in weed areas
X. References
- (2013) Presc Lett 20(8): 46
- Baer (1990) Cutis 46:34-6 [PubMed]
- Gayer (1988) Cutis 42:99-100 [PubMed]
- Epstein (1991) J Wilderness Med 2:183-6 [PubMed]