Background
Toxicodendron dermatitis is an allergic contact dermatitis (allergic phytodermatitis) that occurs from exposure to members of the plant genus Toxicodendron. 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 that produce a similar reaction mediated by different irritant chemicals also exist. See the image below.
Forearm approximately 10 days after exposure to poison ivy in a garden. Note vesicles and linear areas of the rash. Pathophysiology
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. 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 (eg, clothing, pet hair, gardening tools, camping equipment). Although a common misconception, fluid from the vesicles of a poison ivy rash does not contain urushiol and is not an irritant source for new lesions.
Epidemiology
Frequency
United States
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.
International
Toxicodendron dermatitis occurs outside North America. However, the most prevalent form of plant dermatitis worldwide occurs from exposure to the numerous members of the family Compositae and varied sesquiterpene lactone allergens from these plants. With increasing global travel and transport of plants, true toxicodendron dermatitis is being increasingly reported in Europe, although it is still case reportable.[1, 2]
Mortality/Morbidity
Morbidity is related to sensitivity of the individual exposed as well as the degree and route of exposure. Morbidity ranges from localized mild erythema and pruritus to diffuse erythema, edema, severe pain, and pruritus with bullous lesions. Secondary infection can complicate the dermatitis.
Race
No clear racial difference in susceptibility exists.
Sex
No difference in susceptibility between the sexes exists.
Age
Elderly people have reduced sensitivity.
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