Exposure to poison ivy, poison oak, or poison sumac plants results in an allergic reaction of the skin to the plant oil called urushiol.

What is going on in the body?

Not everyone is allergic to urushiol. If the uroshiol from the plant touches the skin of someone who is allergic to it, it starts a reaction that results in blisters. This reaction is known as an allergic contact dermatitis. The outbreak of the reaction starts at the spot on the skin where the urushiol touched it. Once the urushiol has been thoroughly washed off the skin, no further spread of the dermatitis can occur.

Original sites of contact may continue to break out with blisters over the next several days. Portions of the skin that had the most contact usually react first, followed by areas of skin that had less contact with the plant. This often gives people the impression that the dermatitis is contagious, which it is not.

What are the causes and risks of the condition?

Skin contact with urushiol from poison ivy, poison oak, or poison sumac plants causes the allergic contact dermatitis.