Allergic contact dermatitis to poison ivy is often arranged in linear streaks. Not all the dermatitis will appear this way, but vesicles in a linear distribution suggest plant contact dermatitis.

Poison ivy, oak, and sumac share common allergenic catechols called urushiols. The dermatitis they cause is intensely pruritic and can erupt over several weeks.

Severe poison ivy. Intact and collapsed bullae on intensely erythematous skin on the forearm.