It can be picked up on tools, clothing and the fur of pets. Therefore, anything that may be carrying the oil should be carefully washed. Even dead plants may cause allergic reactions for a couple of years. Sensitive people often develop a severe skin rash within hours after contact. Highly allergic people may develop a rash if they inhale smoke when burning poison ivy in brush piles, or if they contact pets with the toxin on their fur.
Some people are more sensitive than others to the effects of poison ivy.
However, sensitivity can change from time to time so that someone who was not affected by it at one time can get a reaction at another time. The plants are most dangerous in spring and summer when oil content is highest. For those sensitive to the oil, a linear rash, resembling small insect bites, will appear within 12 to 48 hours, but a reaction can take up to two weeks to occur. This rash develops into a more severe rash and blisters. Washing with running water is recommended.