Poison ivy, oak, and sumac cause more cases of allergic contact dermatitis in the United States than all other allergens combined. At least 70% of the US population is sensitive to these Toxicodendron species. The allergen urushiol is responsible for Toxicodendron dermatitis, also known as rhus dermatitis. Urushiol is found in many other plants, including in the skin of mangos. Mangos are a common cause of plant dermatitis in subtropical and tropical areas, including Hawaii.
The dermatitis begins with pruritus and erythema, usually within 2 days of exposure in susceptible persons. The degree of dermatitis depends on the patient’s degree of sensitivity, the amount of allergen exposure, and the reactivity of the skin at exposed body locations. The dermatitis may range from erythema alone to papules, vesicles, and bullous eruptions. A linear distribution of cutaneous lesions is strongly suggestive of Toxicodendron dermatitis. This distribution occurs after plant parts have rubbed against the skin or when contaminated fingernails have scratched it.
Poison Ivy. Toxicodendron radicans (poison ivy—shrub or climbing vine). Note that the leaves of poison ivy have three leaflets and the stems are commonly reddish orange. Poison ivy occurs throughout the United States. (Photo contributor: Lawrence B. Stack, MD.)
Poison Oak. Toxicodendron diversiloba (poison oak). Like poison ivy, the terminal part of the branch has a cluster of three shiny leaves. It grows as a tree or woody shrub and occurs west of the Rocky Mountains. (Photo contributor: Ken Zafren, MD.)
Poison Sumac. Toxicodendron vernix (poison sumac). Note that the leaves of poison sumac have 7 to 13 leaflets. It grows as a tree or woody coarse shrub. Only one species of poison sumac is found in the United States. (Photo contributor: Lawrence B. Stack, MD.)
Poison Sumac Dermatitis. A moderately severe local reaction to poison sumac. Note the vesicles, bullae, and exudates characteristic of a contact dermatitis. (Photo contributor: Alan B. Storrow, MD.)
Poison Oak Dermatitis. Erythematous papules and vesicles. This firefighter was exposed to urushiol, the allergen of poison oak, ivy, and sumac, in smoke from burning poison oak. (Photo contributor: Ken Zafren, MD.)
Poison Ivy. Erythematous papules and vesicles in a linear distribution consistent with Toxicodendron dermatitis. (Photo contributor: Alan B. Storrow, MD.)
Management and Disposition
An immediate rinse or shower with warm water and soap may minimize the reaction. If symptoms are limited to erythema ...