History and exam
Key diagnostic factors
common
pruritus
Dermatitis is usually intensely itchy.
Skin feels as if it is burning.
blisters and vesicles
Blisters and vesicles, particularly in linear streaks, are pathognomonic for plant dermatitis.[19]
Arise due to release of urushiols as the plant brushes against the skin.
Most commonly affects arms, face, and legs with sparing of palms and soles.
Hand-transfer of allergen can occur, particularly to the genitals. Some lesions take on the appearance of hand-prints. New lesions may appear for up to 15 days after exposure. Hard-to-reach areas such as the mid-back are rarely affected.
weeping, oozing, and crusting
Signs of acute dermatitis develop 24 to 72 hours after exposure; erythema, edema, vesicles, bullae, weeping, and crusting.
Other diagnostic factors
common
previous exposure
History of previous reactions to poison ivy, oak, or sumac; similar rashes appearing, particularly during the summer months or following trekking or camping trips.
uncommon
breathing difficulties
Rural firefighters have complained of breathing difficulties after inhaling airborne antigen from smoke in forest fires.
generalized erythroderma
With extensive exposure, almost all of the skin can become affected with a generalized dermatitis.
periorbital edema
Can appear when facial contact occurs. Most commonly seen in children, who may encounter the plant at face height.
systemic contact dermatitis
Chicken cooked with Toxicodendron species bark (rhus chicken) is a common traditional remedy in Korea. This can lead to a systemic contact dermatitis 4.0 ± 1.5 days after ingestion. Clinical features include a generalized maculopapular eruptions, neutrophilia, and leukocytosis.[18]
black-spot dermatitis
Black-spot poison ivy dermatitis consists of asymptomatic black lesions on the skin that cannot be washed off. These lesions become pruritic papules, but have been mistaken for melanoma.[20] It may have a specific dermoscopic appearance, namely a jagged, centrally homogeneous, dark brown pigmentation with a red rim. The jagged shape suggests an uneven diffusion pattern of the toxin within the stratum corneum.[21]
Risk factors
strong
occupation that involves exposure to relevant trees and plants
outdoor activities
Direct exposure following hiking, walking, or camping.
use of forestry equipment and machinery
Individuals may be exposed to oleoresins carried on equipment or machinery.
smoke from burning Toxicodendron species
The antigen is heat-tolerant and may travel some distance from the plant by smoke.
children
Peak sensitization to poison ivy, oak, and sumac occurs between 8 and 14 years of age. This may be because children are less likely to recognize Toxicodendron species and are more likely to play outdoors and thus be exposed. Infants are not as easily sensitized as adults.
weak
domestic pets and livestock
Oleoresins can be carried on fur.
genetic susceptibility
Genetic susceptibility to urushiol was suggested by the finding that 80% of children born to 2 urushiol-sensitive parents also became sensitive, but this may reflect common exposure rather than an inherited trait.[16]
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