Poison ivy is a vine or a shrub that is part of the cashew family. It is harmful and it grows in many parts of the United states and southern Canada. You will usually see it twining around tree trunks or on the ground. Sometimes it grows bush-like. There are several species, including poison oak, which grows in the Pacific Northwest and sumac which grows in the eastern United States.

The tissues of these poisonous plants contain an oil (urushiol) that is similar to carbolic acid which is extreme skin irritant. You can become poisoned just by removing your shoes after walking through poison ivy or you can get it from other people — but only if the oil stays on their skin. Remember, it is not the skin eruption that causes the infection, but the oil from the plant. If you come in contact with the plant, wash the skin thoroughly, hopefully to prevent the oil from penetrating and infecting the skin, thereby causing a rash. If blisters do appear, they will be itchy and you can treat them with calamine lotion, Epsom salts or bicarbonate of soda. There is a vaccine that can be taken by injection or orally; as with most vaccines, it must be administered before you encounter the plant.

You can fairly easily identify poison ivy. Its leaves are red in early spring, then change to a shiny green. They turn yellow, red or orange in the fall. Each leaf is made up of three leaflets that have notched edges. Two of the leaflets make a pair and the third leaf stands alone at the tip of the stalk. There are small green flowers that grow in bunches on the main stem close to where the leaves join. In the late season, poisonous berries appear. They are white and have a waxy look.

Poison ivy and oak are so common that it is hard to eradicate them through chemical spraying or other means.