New lesions may continue to appear for up to 2-3 weeks. Poison oak is most common west of the Rockies, poison ivy to the east, and poison Sumac in the southeast. Toxicodendron dermatitis is the most common cause of contact dermatitis in the United States, exceeding all other causes combined. 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. 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.
No clear racial difference in susceptibility exists. A decreased susceptibility in blacks has been reported, but studies on the issue are conflicting. No difference in susceptibility between the sexes exists. In mild cases, classic lesions on exposed skin are secondary to brushing against the plant or excoriations from scratching. Erythema multiforme is an atypical presentation of toxicodendron dermatitis.